As investigators prepare to search a landfill for the remains of missing Phoenix mom Christine Mustafa, her friend is shedding new light on Mustafa’s relationship with the man accused of killing her.

Rebecca Matthews met Mustafa in 2006 when both were students at Paradise Valley Community College. The two became instant friends, spending time shopping, having weekly dessert at their favorite diner, and chatting about their lives.

Matthews says when Mustafa introduced her to Robert Interval for the first time, she “got the creeps.” She says Interval initially moved in with Mustafa as a roommate to help with household bills, but the relationship morphed into a toxic bond.

“She told me 'if anything ever happens to me, don’t question anyone else but him,'” says Matthews. She says Mustafa didn’t always share details about what was going on at home, but she picked up on “red flags.”

“She wasn't allowed to come to girls' happy hours anymore unless he was there,” says Matthews. She also says she’d ask Mustafa about bruises on her body but got excuses that didn’t sit right with her.

When Mustafa disappeared in May, Matthews said she had spoken to her days earlier. She says Mustafa’s sister called her with concerns about where she might be, and Matthews immediately had her suspicions about Interval.

“All this bizarre behavior. Where are you?” says Matthews. “If my partner went missing I’d be there every moment.”

Matthews says Interval seemed to disappear from the public eye, that he wiped out his Facebook page and never helped with search efforts.

Interval sits in jail on first-degree murder charges. He has repeatedly denied requests for interviews. Matthews is fundraising through her business page to help the Mustafa family pay for legal fees.

"If there's anyone out there in a relationship that's abusive, get out,” warns Matthews. “Before it's too late. Because Christine didn't, it was too late.”

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