UPDATE June 7, 2019:

A Maricopa County Superior Court judge sentenced Robert Interval Jr. to 25 years in prison for killing his 34-year-old girlfriend two years ago, The Arizona Republic reports. Her body was never found.

Interval received the maximum number of years the judge could impose.

MORE: Robert Interval Jr. sentenced to 25 years in prison in girlfriend's death, despite lack of body - The Arizona Republic

November 17, 2017:

A generous young mother with everything to live for. So when it appeared Christine Mustafa walked out on her job and her precious daughters, everyone feared the worst. Cops say she didn't. And now a desperate search is on to find the mother of two.

Christine's parents had immigrated to the United States from Jordan. And before long Christine was living the American Dream.

"She purchased a house on her own as a single mom," said Christine's friend Rebecca Matthews.

Family friend Erin Neathery says that when Christine gave birth last year, no one worried if she'd be able to juggle two daughters and a full-time career -- least of all, her employer.

"She had worked there for 11 years and never missed a day," said Erin.

But in May the new mom disappeared.

"She was nowhere to be found," said Erin. "This was unusual."

After a couple hours and still no Christine, her family called Phoenix Police to do a welfare check at her house. Christine's car was in the driveway, but no one answered the door. That's when cops broke in.

"She left her passport, her purse, her cellphone, her car, her clothing, her children," said Erin. "It was very clear that something was very, very, very wrong."

As police searched the house, Christine's live-in boyfriend and father of her new baby showed up. Robert Interval had moved in with Christine Mustafa not long after she bought her home.

"She decided 'A roommate would really help me out to pay these bills,'" said Rebecca Matthews.

Christine placed an ad on Craigslist for a roommate, and the handsome former model answered. Now the roommate-turned-live-in-lover was answering cops' questions.

Robert Interval told cops Christine's car had a flat tire that morning, so she walked to work, a detail that would later provide a key clue in the investigation.

Erin Neathery knew Robert Interval before he moved in with Christine Mustafa. She says he could be quite charming.

"Very friendly, outgoing, helpful to a fault," said Erin.

Soon Christine was pregnant with Interval's baby. But not all was rosy. Interval had grown increasingly controlling, according to friends, even convincing Christine to move near his family. They left Arizona.

"Robert convinced her to move to Ohio for a fresh start near his sister," said Erin.

But Christine's family wondered if there was a different motive. They'd seen a different side of Interval.

"They felt that it was more a move to separate her from her family and isolate her," said Erin.

If that was Interval's goal, it didn't work. And the family's concerns were real. While he looked like a gentle, doting dad, Christine's friends claim he could be a Jekyll and Hyde.

"Robert could go from very happy and joking and it was like -- boom -- a light switch went off and suddenly dark and anger," said Erin.

Erin says living in Ohio with their new baby actually gave Christine motivation to finally want out.

"She wasn't happy with raising a baby in that environment," said Erin Neathery.

So Christine moved back to Arizona near family. And what she did next may have put the young mom in grave danger.

Rebecca Matthews will never forget the last text she sent her best friend Christine Mustafa.

"I sent her a text message right then and said 'Babe, is everything OK?'" Rebecca tells Crime Watch Daily.

She didn't expect a reply. She already knew everything wasn't OK.

"Christine never missed a day of work," said Rebecca. "And then all of a sudden she doesn't show up?"

May 11, 2017 Christine Mustafa vanished. And friends say it's what the mother of two was about to do that very day that may have triggered her disappearance.

"She was going to also get a restraining order," said family friend Erin Neathery.

Christine wanted her live-in landscaper boyfriend Robert Interval, the father of her baby, out of her life.

"She was so close, she was so close to getting out, but she never made it," said Erin.

From the moment cops arrived at her home, Interval's story just didn't add up. He claimed she had a flat tire and walked to work that morning.

"Her work was miles across town," said Erin. "There's no way you could walk, let alone in that heat."

And when cops checked the car, there was no flat tire at all. Then came Interval's suspicious behavior. Suddenly he'd put a bunch of Christine's things up for sale.

"I was flabbergasted," said Erin. "Robert had put up Christine's car for sale, his landscaping truck for sale, there were items from the home that were for sale."

Suspicious investigators returned the next day to some surprising finds.

"Robert answered the door with a loaded gun, and the baby," said Erin.

Cops removed the gun from Interval's pocket. And after seeing his daughter's bedroom, the Department of Child Safety removed her from the home. Inside was a disturbing clue.

"It was very evident that there had been used bleach spray, you know, it bleaches the paint," said Erin Neathery.

Interval's explanation only raised police antennae even more. He tells cops that a day earlier he had no choice but to give the baby's room a thorough cleaning with bleach.

"He made some excuse about the baby having bedbugs in her room," said Erin.

But DCS investigators didn't buy it. They'd uncovered so many red flags from the relationship, including a terrible account told by one of Christine's sisters to Crime Watch Daily Phoenix affiliate ABC15 KNXV-TV.

"He literally pulled her by her hair, shoved her out of the car shoeless, purse-less, phoneless. She was helplessly running down the street begging for help," Christine's sister Suzanne Wong told the station.

Now Christine Mustafa was missing and Robert Interval was the main person on cops' radar. Interval's sister Gia flew to Arizona to be with her brother. It turned out to be a very short visit.

"It was too much for her," said Rebecca Matthews. "Robert's sister flew back to Ohio because she couldn't handle it."

What couldn't Gia handle? Believing her brother had killed Christine. That's exactly what she suspected after a chilling conversation with Interval himself. Gia says the one-time model admitted a big fight started with Christine after she threatened to leave him. She claims he then repeatedly said:

"'I've taken it too far and I've seen things I can't unsee,'" said Rebecca.

"What that means is just too frightening to even comprehend," said Erin.

Whatever it meant, it was enough for cops to get another search warrant. This time they found what's believed to be physical evidence of foul play inside the couple's home.

"It's our understanding that there's blood in both the baby's bedroom and her bedroom," said Erin.

Cops say a phone was found in the bathroom between the toilet and bathtub.

"Maybe she went in the bathroom to call for help and he busted in," said Rebecca Matthews. "I believe that she was trying to call for help and he made that impossible."

Though cops found blood and other evidence, they still didn't have a body. That's when hundreds of volunteers joined the Mustafa family to search.

"Sometimes 10 people would show up, sometimes 30 or 40 people would show up, but this is all in triple-digit heat in the middle of Arizona summer," said ABC15 Reporter Sonu Wasu. She says finding the mother of two became a citywide effort.

"They were friends, neighbors, co-workers, even those who didn't know her, they want to know where Christine is, what happened to her," said Wasu.

But Rebecca says there was one person who didn't seem concerned about finding Christine: Her boyfriend Robert.

"Robert was nowhere to be found," said Rebecca.

Weeks of searching came up empty. But on the one-month anniversary of Christine's disappearance, cops felt they had enough evidence to arrest Robert Interval and charge him with her murder.

"We do have some evidence that does point to Robert as being a suspect," said Phoenix Police Sgt. Alan Pfohl. "He was also the last person to see Christine, and I think he's the one that really has these answers."

"It was a little release of fear, because there was so much fear that he was going to get away with it completely," said Rebecca.

"The baby was there, which breaks my heart at what she may have witnessed," said Erin Neathery. "I just can't imagine, but it's not good."

In July, cops released more critical clues.

"There is a landfill in west Phoenix where we believe Christine to be," said Sgt. Pfohl.

Evidence suggests Christine Mustafa was killed inside her home on May 10. Police suspect Robert Interval then dumped her body in a nearby trash container.

"We have the area that we believe her to be pretty well-identified," said Sgt. Pfohl.

Although he's hopeful Christine can be found, Pfohl admits there are no guarantees.

"While it's our greatest hope to find Christine, we also tell the family not to get their hopes up because this is a very difficult task," said Sgt. Pfohl.

Sadly, Christine's disappearance isn't the first tragedy to strike the Mustafa family. She is the third daughter they've lost.

"One of Christine's sister's several years ago was murdered," said Rebecca. "In December another one of their sisters died of cancer."

And to add to this family's heartbreak, they can't get custody of Christine's baby daughter, one of their strongest living links to Christine. With her father Robert Interval behind bars, the child remains in protective custody.

"Robert has parental rights, Christine's not here, so she's considered to have abandoned the child," said Erin. "Christine's sisters go and see the baby as often as they are allowed to."

The Mustafas want full custody given to Chrstine's twin sister, who's also now raising Christine's teenage daughter.

"Robert wants her to go to his sister," said Erin.

Right now the law is on his side. But Erin says Christine's family will never quit fighting for custody -- or for justice. Because it's what Christine herself asked them to do.

"Christine told her sisters 'If ever I go missing, go and get my baby, find Rob and get my baby. Fight for her, don't let this stand,'" said Erin Neathery.

Robert Interval has pleaded not guilty to one count of first-degree murder. His bail was set at $1 million. His attorney says he'll ask the judge to reduce bond to $100,000, claiming the evidence against Interval is insufficient.

UPDATE June 7, 2019:

A Maricopa County Superior Court judge sentenced Robert Interval Jr. to 25 years in prison for killing his 34-year-old girlfriend two years ago, The Arizona Republic reports. Her body was never found.

Interval received the maximum number of years the judge could impose.

MORE: Robert Interval Jr. sentenced to 25 years in prison in girlfriend's death, despite lack of body - The Arizona Republic