The calm of a Christmas Eve in Milwaukee, Wisconsin is interrupted by gunfire. Five shots, one target. Officer Jennifer Sebena had just come back from a break when she was ambushed from behind.

It's barely Christmas Eve 2012 in Wauwatosa, Wisconsin when five shots shatter this pretty police officer's silent night.

"She was ambushed from behind and ultimately she was shot two times in the back of the head," said Lt. Zalewski.

But Officer Jen Sebena's killer wasn't done.

"He took her gun right out of her holster while she laid on the ground and shot her three times in the face," said Lt. Zalewski.

Her broken-hearted husband erupts in rage as her brothers in blue track her killer's footprints in the snow.

Jen Sebena, 30, was married, by all accounts happy, and didn't have an enemy in the world. Fellow officers say she was the kind of cop most people actually loved to see coming.

"Her smile was infectious around the station," said Wauwatosa Police Officer Brian Zalewski.

"Just a very good person who wanted to help people," said retired Wauwatosa Police Lt. David Moldenhauer.

In or out of uniform, Jen Sebena was always there for people. She even served as church leader in a youth group.

"She had like a group of girls that she would just keep track of, keep tabs on, but you never felt like you were just a number in her life book," said Jen's friend Maggie Ross. "She always made you feel like you were her favorite. She was the most fun-loving, caring, energetic person than you ever would meet."

Her husband, Ben, a Marine and Purple Heart war hero, was seriously injured in Iraq.

Ben spent months in the hospital. In a YouTube video done for his church, Ben credits Jen with saving his life.

"I came back home to Wisconsin and starting spending more time with Jen, and our love flourished," Ben Sebena says in the video.

Just hours before her murder, Ben texted his wife to wish her Merry Christmas. She writes back, and few minutes later Ben texts Jen again: "Well call me if you get too bored! I love you. Merry Christmas."

Jen writes back: "I love you too :)"

A little more than five hours later, Ben texts Jen again -- this time there is panic in his words: "Baby are you OK? They just said an officer is down in Tosa?"

Jen does not respond. Nine minutes later Ben sends another text: "Baby, please text or call me. I'm scared."

Still no response at 5:51 a.m. Ben sends one last desperate message: "Babe Please"

Minutes later Ben calls the Wauwatosa Police Department in a panic. Dispatch can't reach Jen either.

The department quickly tracks her squad car to the parking lot of the fire department, where police officers would often park to fill out paperwork. Cops from Jen's watch were first on the scene.

It took only minutes for her fellow officers to get there, but when they found her it was already too late.

"I can't imagine what those officers immediately went through when they came upon her in that parking lot," said Lt. Zalewski.

Officer Jen Sebena had been shot hours earlier. The attack was calculated and cold.

"She was laying in a cold, wet parking lot. She was shot multiple times in her head and in her face. It's just not right for her to have been left like that," said Lt. Zalewski. "That's not a normal homicide.

"There was no indication based on the medical examiner's report that Jennifer wasn't dead from the first two rounds that were fired. There was no reason to remove her gun to shoot her in the face," said Zalewski.

But who would be so vicious to this loving wife and beloved police officer in the early morning hours of Christmas Eve?

"It clearly indicates that it was very personal," said Zalewski.

Cops started tracking footprints in the snow found in the parking lot as detectives deliver the tragic news to her husband Ben at the station.

"He was visibly upset. He was emotional as you would expect him to be," said retired Wauwatosa Police Lt. David Moldenhauer.

"She was a wonderful person. She was helping me. She was always helping me," Ben was recorded on tape in the station.

Just hours before Jen was assassinated, Ben tells detectives he kissed his smiling wife goodbye for the last time.

"She was happy. We hugged, we had a big hug and a kiss," Ben Sebena tells investigators.

Cops are baffled. Then a break that would turn this case upside down.

Detectives start checking surveillance cameras in the area around the shooting. Suddenly they spot a familiar vehicle: a black Prius, with black rims.

"His vehicle is basically tracked through Department of Transportation cameras from locations up near their residence, and all the way down through the freeways and through the side streets to where it appears on camera a block away from the murder scene," said Zalewski.

Officer Jennifer Sebena was gunned down while on patrol in the suburbs of Milwaukee on the early morning of Dec. 24, 2012. Jen Sebena was ambushed, shot five times, with three bullets to the face.

"In my head, I was obsessed with the fact that she was lying out in the rain," said retired Wauwatosa Police Capt. Jeff Sutter. "And I couldn't get out of my head. It ate me alive for months after the fact, that she was lying out in the rain, alone."

Her brothers in blue are heartbroken.

"I looked at all of the younger officers almost like my kids, and tell all the families how we were going to keep them safe, and I failed. I failed miserably in this case," said Sutter. "I didn't keep her safe."

And when they deliver the news to her husband at 7:03 am that morning, he's inconsolable, turning over a table in the police station in an outburst.

Wauwatosa police are baffled. Officer Sebena seemed to be loved by all. Could there be a crazed cop-killer on the loose? Investigators don't think so. The three shots to the face tell them something different.

"It clearly indicates that it was very personal," said Lt. Brian Zalewski.

Police track footprints in the snow at the scene. At first it leads nowhere. Then a break. Detectives begin checking surveillance cameras in the area around the shooting. Suddenly they spot a familiar vehicle: a black Toyota Prius with black rims.

Who is it? Unbelievably, the Prius looks identical to the one Jennifer's husband Ben drives.

"His vehicle is basically tracked through Department of Transportation cameras from locations up near their residence and all the way down through the freeways and through the side streets to where it appears on camera a block away from the murder scene," said Lt. Zalewski.

Ben Sebena was called back down to the station. It's 4:30 in the afternoon on Christmas Day. He rushes over without hesitation. Ben's there to get answers about what happened to his wife -- instead, he gets questions.

Detective: "Ben, something happened that morning and only you know what happened there."

Ben Sebena: "I do not."

Detective: "Ben."

Ben Sebena: "You're upsetting me with this."

Detective: "I don't mean any disrespect."

Ben Sebena: "What I need to explain to you is that I loved her. There was no rage, there was no outburst ever directed at her, and I never would. Because I had such true love for her that I couldn't hurt her."

Despite Ben's denial, cops go to Jen and Ben's house. They find footprints in the snow there too, but at first they come up empty inside. Detectives go back to grilling Ben later that Christmas Day.

"I could never have hurt her," Ben tells investigators. "If I was there I would have saved her ass. I would have stopped it. I would've done anything to stop this from happening."

"He made so many different statements that it's difficult for me to really gauge how much of it was true and how much of it wasn't," said retired Wauwatosa Police Capt. Jeff Sutter.

Now convinced Ben's the killer, police go back to the house again for a closer look. This time they hit the jackpot, literally finding the smoking guns stuffed in the ceiling.

"Hidden behind several pieces of insulation in the rafters of the basement we located both the 9-mm Makarov-style weapon and we located Jennifer's duty weapon," said Lt. Zalewski.

Cops soon learned Ben Sebena was hiding another very dark secret. In a YouTube video made by his church before Jennifer's murder, the former Marine who fought in Afghanistan and Iraq, reveals he's now battling post-traumatic stress disorder (PTSD).

But was his dark and lonely world so bleak it made him kill the one person who loved him unconditionally?

"I wonder when he kissed her goodbye when she went to work that night, did he have an idea that this was going to happen?" said Wauwatosa Police Chief Barry Weber.

"I think the war and PTSD did make a contribution to his acting out and murdering his wife," said Dr. Ashok Bedi. "However, I don't think that was sufficient enough explanation."

Dr. Ashok Bedi, a board-certified psychiatrist for more than 40 years, is an expert on PTSD. He never interviewed Ben Sebena, but after looking at the case he tells Crime Watch Daily he thinks Ben was afraid of losing Jennifer.

Prosecutor Mark Williams claims Ben Sebena was insanely jealous and angry about his wife's success as a police officer.

"One of the things that no one knew until he told us is that he had been stalking her. And he said that a lot of this was because of the jealousy was motivating him. He wanted to find out what he was doing. He obviously made a choice at some point that he would have to kill her in order not to lose her," said retired Milwaukee County Assistant District Attorney Mark Williams.

"Jennifer was very professional, she was friendly but never flirtatious with anybody that I saw," said Barry Webber. "He was struggling in his own life as far as to get a successful career or job , and of course she had hers all laid out. So I think that was a source of friction probably between them."

Jennifer Sebena had only been with the department for a little less than two years, and in public she and Ben seemed to be a married couple madly in love.

"My first encounter with him was actually at Jennifer's swearing in, and the two of them were like giddy teenagers in love, in all outward appearances, holding hands and giggling and staring into each other's eyes," said Sutter.

Remember, when cops first told Ben Sebena about his wife's death, he flew into a rage. Now cops believe Ben was just trying to throw them off his track.

"He flipped over the interview table in a fit of rage and I think that was just something he probably thought would be appropriate or something that somebody who just found that out would do. I don't think it was because he was that angry or that upset," said retired Lt. David Moldenhauer.

Finally at 6:52 the day after Christmas, following 60 grueling hours of interrogation, Ben Sebena comes clean.

"Confession time, right? I did it," Ben Sebena tells detectives. "I did it."

He confesses to shooting the woman he claimed to love: Twice in the back of the head, then pulling out her very own police pistol and firing three more rounds right into her face.

"I can only hope that it was quick, that it was painless, that her last thoughts were nothing but positive, happy as she walked out of that fire station, ready to continue on her shift, ready to keep doing the job that she loved," said Lt. Zalewski.

And the former Marine war hero now sat calmly describing the vicious attack to the same detectives his beloved wife used to call her brothers in blue.

Ben Sebena's interrogation was recorded on camera.

Ben Sebena: "I shot her and she went down. And I went up to take another shot and she started getting up and she started going for her gun so I went for her gun, and then I shot her with the second pistol again, and then I grabbed the other one and shot her a couple more times just to make sure she was actually out."

Detective: "Do you think she knew it was you?"

Ben Sebena: "I don't think so."

Ben's cold confession sends a chill through Jennifer's fellow cops.

Detective: "Why did you shoot her in the face with her own gun?"

Ben Sebena: "That was just because I wanted to make sure she was dead."

"He took the extra time and effort to remove her gun out of her duty holster and while looking down at his wife shot her three times in the face," said Lt. Zalewski. "That's personal. That means something, that's premeditated."

Jennifer Sebena's active-duty death is the first ever on-the-job killing in the Wauwatosa Police Department's 96-year history.

On the day after Christmas, after 60 grueling hours of police interrogation, Ben Sebena finally caves.

"It's confession time, right? I did it," Ben Sebena says.

During his interrogation, Ben Sebena shocks detectives again, telling them he was the one who was supposed to die.

Ben Sebena: "I wish I could have just killed myself."

Detective: "Why didn't you?"

Ben Sebena: "Because she would have killed herself after that."

Believe it or not Ben claims that's the reason he executed his wife. In his warped reality, Ben tells detectives he believed that if Jennifer killed herself, she would go to Hell.

"Part of me wanted her to be in Heaven. I didn't want her to dealing with this s--- anymore. It was just too much for her," Ben tells detectives.

But Dr. Ashok Bedi, a board-certified psychiatrist, has a hard time believing Jennifer Sebena's vicious murder was a "mercy killing."

"A lot of hatred," said Dr. Bedi. "If you want to make sure someone is not suffering, you shoot them in the heart. As a soldier he would know that, that shooting someone in the face is not the way to kill someone. That's anger."

And Ben Sebena showed a terrifying glimpse of that anger when detectives left him alone in the room with the camera still recording. He addresses the camera.

"If they ever make a stupid documentary, this is the photo that they're going to take," Sebena says to the camera in the empty room. "'The mind of a killer.'"

Ben Sebena was charged with first-degree intentional homicide. He first pleaded not guilty. Then he changed it to not guilty by reason of insanity.

"What the defense has to prove is that Benjamin could not determine right from wrong," said retired Milwaukee County Assistant District Attorney Mark Williams.

Cops say everything Ben Sebena did after gunning down his wife proves he knew the difference: Running from the scene, hiding the guns, denying it through 60 hours of interrogation.

"He came across as somebody who felt as though he was gonna get away with this. He believed he was smarter than everybody in the room," said Lt. Zalewski. "He believed he was smarter than everybody on this police department, up until the point that he confessed."

Ben Sebena eventually changed his plea in court to plead guilty to first-degree intentional homicide.

Ben Sebena's mother pleaded with the judge to remember her son was sick.

"Our military is skilled in training our young men and women how to fight and to kill. But when their service contracts are fulfilled and they come back home, they fail to teach them how to live again," she said in court.

And Ben Sebena's parents sent an impassioned seven-page letter, writing in part: "We ask for mercy. Ben in his illness thought he was helping his wife."

Then just before sentencing, Ben Sebena offered his apology to Jennifer's family.

"I'm in a place where I didn't have anything else left for me. And after our discussion, I didn't want to do that to her, and I'm sorry that I took away your daughter and I'm sorry I took away your sister. If I could replace my life with hers right now, I would do it."

The judge sentences Ben Sebena to life in prison without the possibility of parole for 35 years.

"Mr. Sebena will be about 65 or 66 years old when he is allowed to petition for release," the judge read in court

"The fact that Jennifer was such a good person, and through our investigation we learned that Ben was truly an evil person," said Moldenhauer. "It's not like this was a crime of anger in the moment, a crime of passion in the moment. This was a calculated, evil person, laying in wait for somebody that they supposedly loved and then just completely, violently killing her."

"I just wonder if every day if he stops to think about what happened," said Wauwatosa Police Chief Barry Weber. "I hope so, because he destroyed something beautiful for whatever reason, and not a good reason."

Jennifer Sebena seemed to love everyone, and everyone seemed to love her. She only served as an officer for two years, but she touched so many hearts, especially those behind the Wauwatosa Police badge.

In honor of Jennifer Sebena's service, her name was added the National Law Enforcement Memorial in Washington, D.C. Also her fellow officers in Wauwatosa, Wisconsin have dedicated a memorial to her at police headquarters.