Every year 240 million calls are made to 911. And oftentimes that conversation can be the difference between life and death. Such was the case when Deanna Cook picked up her cellphone and frantically pushed those three buttons.

Warning: The 911 call you are about to hear is very disturbing. On it you can hear Deanna Cook pleading for her life as she's attacked in her home.

The story of Deanna Cook's tragic Dallas death has sparked major changes in the way all emergencies are now handled in the state of Texas.

Deanna Cook was stunning, vibrant and athletic. Since an early age, Deanna was always running.

"She loved to run. I used to tell her all the time, 'You get upset, just run. When things don't go your way, just run.' Broke records in the 200-yard dash, when she was in the 7th grade, she broke a record," said Vickie Cook, Deanna's mother.

Not just a star on the track, Deanna was the constant center of attention in her tight-knit family in Dallas.

"When she came in, she was going to be the star of the show," said Deanna's sister Karletha Gundy. "She was just a really fun person. She was always on like 10."

But the brassy beauty had a gentle side too with her love for animals -- and especially her two young daughters.

Deanna raised her girls on a middle-class street in South Dallas.

"She moved there because it's a nice area," said Vickie Cook.

But I can tell you firsthand having grown up in a rough part of town nearby, the dangers of this area were never far away -- dangers Deanna could never run from.

When Deanna suddenly goes off the radar, her mom Vickie knows something isn't right.

"August the 17th [2012] was a Friday," Vickie tells Crime Watch Daily. "She usually called me around 10 or 11 every day when she'd be driving for her job, and this particular day she didn't call."

By Sunday morning no one in the family has heard from Deanna.

"I said 'That's not like Deanna,' I said, 'and she hasn't called me,'" said Vickie. "I said 'So can y'all please help me try to find Deanna?'"

After church Vickie enlists Deanna's daughters, who'd been staying with Vickie, and Deanna's sister Karletha to check on her.

"We knew something was wrong, but I don't think we were expecting what we found," said Karletha.

At first, there's no clue that something is amiss. Deanna's house is quiet, but there's no sign of Deanna.

"We kind of tried to peep in windows, tried to knock on the front door, knock on windows, we couldn't get in, couldn't see in," said Karletha. "The blinds were kind of like frayed a little bit but we couldn't see anything."

But then, something odd: a river of water gushing from the garage out to the gutter.

Deanna's mom Vickie reaches out to authorities for help, and calls 911.

"I called 911 and I told them I needed someone to come because I hadn't heard from her in three days and the dogs was barking and nobody's coming to the door, and I needed the police to come," said Vickie.

But the operator insists that police are a last resort.

911 operator: "Have you called all the jails and hospitals?"

Vickie Cook: "No I have not. Ma'am, can you just send the police over here?"

911 operator: "No ma'am, you just have to do this first."

"I kept telling her 'I don't know what you're talking about, I need someone to come here now,'" Vickie tells Crime Watch Daily.

"That's when I said 'Hang up that phone, mom, I'm about to break down the door,' and so I just turned around and kicked the door, and on the third kick it flew open," said Karletha.

Inside was an odor so overpowering and ghastly that Karletha retches and covers her nose.

"I've never smelled death before," said Karletha.

"The house was like clean, but it was water everywhere," said Vickie. "And I was howling 'What's going on, what's going on?'"

Vickie, Karletha and Deanna's daughters follow the stream flowing from the back of the house.

"Her door to her bedroom was like closed, so I took my fingers and I like pushed it," said Vickie.

"And it fell off the hinges, and then that's when we saw the bedroom," said Karletha.

Deanna's room was trashed, the scene of a brutal fight.

"Her table in her room was flipped over, her jewelry was everywhere, it was like a mess," said Aniya Williams.

"Her room was bombarded, that's what it looked like," said Neycea Williams.

Vickie Cook: "Something happened in here! Her room is tore up!"

911 operator: "OK ma'am, I'm sending police. Don't -- I need everybody back outside."

But inside the attached bathroom was something worse -- something truly horrible and haunting.

Vickie: "Oh my God!"

911 operator: "What is it?"

Vickie: "Oh my God! Oh my God!"

911 operator: "Ms. Cook, did you find her? Ms. Cook? Ms. Cook! Ms. Cook!"

Vickie can't answer. What she saw left her sickened beyond words.

"I walked in the bathroom and I pushed the door open and I seen her in the water and I screamed, and it was like, it was -- I saw Deanna in that water. Oh God," said Vickie.

Through her tears Vickie has an uncontrollable surge of rage.

"I just started screaming 'He did it, he said he was gonna do it and he did it. He did it,'" said Vickie. "No question at all. But I had strength from God to keep me from doing what I wanted to do -- Go kill him myself."

Warning: The 911 call is very disturbing.

Deanna Cook has been found by her family, strangled, drowned and decomposing in a running bathtub.

That picture still haunts Deanna's family, and so does another 911 call that came in just one day before she was brutally murdered.

911: "Dallas 911, this is Pat, what's your emergency?"

Deanna Cook: "Um, I have a stalker."

And there were a lot more chilling calls for help.

Deanna Cook: "He's been out here and he's parked all day long, sitting out here across the street watching my house. I don't know what his plan is."

Deanna Cook lived in fear for years.

Deanna Cook: "If you can look up my name you could see about a hundred, thousand, probably a thousand complaints, but ain't nobody doing nothing."

Deanna's mother claims that day the cops didn't consider the call an emergency.

"I told her to call the police and she said that she did, but they won't do anything," said Vickie Cook.

Deanna Cook made her last 911 call on the day of her murder, and we have to warn you: It is terrifying.

911: "Dallas 911, what is your emergency?"

Deanna Cook: "[Screaming] Stop it! Stop it!"

911: "Hello? Do you need police, fire or ambulance? I need an address."

"Deanna is not in a position to talk to the 911 operator. She's being attacked, she's fighting for her life," said Trey Stock, assistant district attorney, Dallas County, Texas.

Deanna Cook: "What is wrong with you? Stop it!"

"And she was angry, but as the call goes on Deanna becomes far more fearful, and Deanna is petrified," said Stock.

Deanna Cook: "Please, I'm not doing nothing! Please, baby! Please Delvecchio. Delvecchio, please. Please don't take me out. Please. Don't take me out, please."

Delvecchio Patrick is Deanna Cook's enraged ex-husband. He has no idea every second of his brutal attack on Deanna is being recorded on her cellphone in a call to 911.

Delvecchio Patrick: "Where the police?

Deanna Cook: "I'm not doing nothing to you!"

Delvecchio Patrick: "Where the police?"

"'Where's the police now?' As though 'There's nobody here to help you now, where's the police?'" said Trey Stock. "And of course he flat out, 'I'm gonna kill you.' Over and over."

Deanna Cook: "No!"

Delvecchio Patrick: "I'll kill you. I'm gonna kill you. I'm gonna kill you."

Then, horribly, Delvecchio Patrick makes good on his sickening threat, and chokes the life out of Deanna Cook.

"You hear her like gasping for air or choking. You hear the water in the background and then it goes silent," said Karletha Gundy.

Silence for 15 more horrifying minutes. Until finally:

911 operator: "Hello, ma'am, do you need police, fire or ambulance?"

Tragically, this was not Delvecchio Patrick's first act of violence against Deanna. Cops uncovered a long and terrifying history of abuse.

Deanna's family worried about Delvecchio from the very start.

"Before they even got married, he used to beat on her, but she married him because she thought she could help him," said Vickie Cook.

She thought marrying would change things.

"He would stop," said Vickie. "It got worse."

Worse, including a night of explosive violence that saw a jealous and enraged Delvecchio beating Deanna senseless, and in a hint of things to come, choking her unconscious.

"And when she woke up she, all of her clothes were gone, he had removed her clothes, and she ended up running out the house to a neighbor's house," said Karletha.

He could have killed her that day.

"He tried," said Vickie. "That was the third time."

It's the latest in a long list of assaults that send Delvecchio to county jail time and time again.

"He would go to jail for days and get out," said Karletha.

Finally, Deanna has had enough. She divorces Delvecchio and files papers to keep him away.

"She had an active restraining order on him," said Karletha.

But Delvecchio's threats never stopped.

You heard Delvecchio threaten to kill your daughter?

"I did. I did and I told her to leave him alone. I said 'He's serious. He's gonna do it,'" said Vickie.

The 911 operator isn't sending help.

911 operator: "Hello, ma'am, do you need police, fire or ambulance?"

That has many people asking, including the district attorney: If this isn't an emergency, what is?

"It took too long for a unit to be assigned. It took too long," said Dallas County Assistant District Attorney Trey Stock. "The unit didn't arrive I believe until 50 or so minutes after the call was made."

Fifty minutes too late to save Deanna Cook.

"It was like they wasn't in a hurry. They didn't care. They didn't care. They didn't care," said Vickie Cook.

One of the reasons it took so long is because Deanna called the 911 operator on her cellphone.

"If it's a land line they can know exactly where the call is coming from and they can send out units," said Stock. "She's trying to figure out where this call is coming from and so she's having to look back through prior calls and prior history to figure out the location of the call."

When officers do finally arrive, they knock, look in the windows, and when they get no response, they leave.

"Why critical information wasn't relayed to officers, and why this call didn't receive the priority it deserved, I don't know exactly why," said Stock. "You know, we failed Deanna, all of us, we all did in some respect."

Would the same system that failed to save her life bring Deanna Cook justice?

"My job was to hold Delvecchio Patrick accountable, and so I really was really trying to make the focus on him," said Trey Stock.

Delvecchio stands before a jury, charged with first-degree murder. He pleads not guilty.

His defense? That Deanna had a history of drug use, and what the 911 call recorded was Deanna hallucinating that Delvecchio was attacking her.

"He was cold," said Stock. "Delvecchio Patrick was a controlling, jealous sociopath. He wanted to control Deanna more than anything else, and if he couldn't control her he was going to kill her."

But when Deanna's mom Vickie Cook takes the stand, her pain is very real. You can hear a pin drop as Vickie again lives through the horrible memory of finding her eldest child dead.

Court takes a break, allowing Vickie to compose herself. But when she returns, she's seething as Deanna's final 911 call is played.

"I wanted the tape to play over and over so he can hear her scream and he can hear what he did and get some kind of remorse from that, because he didn't have any when we was in court," said Vickie.

Deanna's haunting voice from beyond the grave sent shivers through the jury. And it seals his fate. Delvecchio Patrick is found guilty of first-degree murder.

And if there is any lingering doubt about the devil that took Deanna's life, Delvecchio's horns are on full display during the victim's impact statement.

"When Deanna's daughter was giving her statement, Delvecchio gave her the finger," said Trey Stock.

"He's a person with no feelings, no soul, no conscience. Like he belonged to the devil," said Vickie.

The judge takes notice, and hammers Delvechio Patrick with a virtual life sentence: "Assess his punishment at confinement in the institutional division of the Texas Department of Criminal Justice for 85 years."

Despite the conviction, the family has now filed a civil suit against the city of Dallas.

Outrage at Deanna Cook's tragic death has already led to change. The city completely revamped its 911 emergency response system.

"There were massive changes to the system after this case," said Trey Stock. "Staffing has been increased by a large margin. And I also know that domestic violence calls like this are given a higher priority, and they deal with these calls with more urgency at the 911 call center."

And Deanna's family, while still reeling from her savage murder, created a foundation in her name called Deanna's Voice.

"We have events, we have a scholarship fund, a program called Breaking Barriers, that's basically giving back to those families who unexpectedly are also victims like we were victims," said Karletha Gundy. "We called it Deanna's Voice so that we can shine a light on those people that voices are being taken from them."

If Delvecchio Patrick is watching the show, what would you say to him that he needs to know from your heart to his?

"I forgive you," said Vickie Cook. "I hate you did what you did, but I forgive you because I can't make it to Heaven with hatred of you in my heart. So I have to forgive you."

The 911 operator who took Deanna's call says she was forced to go into hiding after her name was made public. In an interview done shortly after she left her job, she revealed she herself was a survivor of domestic violence.