PHOENIX (3TV/CBS 5) -- Linda Donaldson was in the courtroom Tuesday when a jury convicted a man for the murder of her sister, Christine Mustafa.

But she doesn't quite feel like justice is being served.

"One day he (Robert Interval) will be free," Donaldson said. "I don't think it's fair to where he took my sister. He didn't give her that same option. Why should he be able to have that option to walk free?"

[READ MORE: Jury finds Robert Interval guilty of second-degree murder in Christine Mustafa case]

Interval was accused of first-degree murder for the death of his girlfriend, whose body has never been found.

Mustafa disappeared in May of 2017.

Mustafa's friends and family were convinced the Phoenix mom was brutally killed in a premeditated fashion and deserved to be locked up for life.

But without a body and no murder weapon, jurors convicted on a lesser charge of second-degree murder.

[WATCH: '[We did] the most justice that we could come up with,' says juror on Robert Interval trial]

Rebecca Matthews was one of Mustafa's best friends.

[RELATED: Friend sheds light on relationship between missing Christine Mustafa and accused killer (Oct. 20, 2017)]

"That's the thing; nothing will bring her back," she said. "Yeah, he's going away for a long time, but she's never coming back. She didn't deserve this. She was the most kind person I'd ever met in my entire life ."

The trial lasted for nearly two months with prosecutors describing Interval as a jealous, controlling man who was afraid Mustafa would leave him and run off with their young daughter.

Defense attorneys argued there was a lack of evidence and nothing to prove Mustafa is even dead.

One juror said their two days of deliberations were extremely difficult, but he believes they did the right thing.

"It was very hard for the whole jury to hear and witness," the juror said. "What we've done here is the most justice that we could come up with."

The jury also determined that there were aggravating factors in this case.

Among those factors, Interval lied to police, tried to cover up the crime, and never showed remorse.

A sentencing hearing has been set for June 7.

Interval is facing between 15 and 29 years in prison.

Jason Barry is best known for his Dirty Dining Report which airs Fridays at 6:30 p.m. on CBS 5.  He is also the storyteller behind CBS 5's Pay It Forward which airs every Thursday at 6:30 p.m.

Copyright 2019 KPHO/KTVK (KPHO Broadcasting Corporation). All rights reserved.



Jason Barry is a nine-time Rocky Mountain Emmy Award winner who is best known for his weekly Dirty Dining reports highlighting local restaurants with major health code violations.

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