DID A SON HAVE HIS PARENTS MURDERED SO HE COULD LIVE A RITZY LIFESTYLE? HIS SISTER SAYS THERE IS NO WAY HE DID IT

48 HOURS Investigates in "A Sister's Fight for Her Brother" on Saturday, May 15

After Scott and Janet Pettit were found dead in their Modesto, Calif., home in 2013, their son, Brandon, was accused of hiring a friend to kill them. Investigators maintained that he wanted his parents' money to start a new life. His sister says her brother loved their parents and there's no way he did it. She vows to fight for his freedom.

Correspondent Erin Moriarty and 48 HOURS investigate the death of the Pettits and the case against their son in "A Sister's Fight for Her Brother" to be broadcast Saturday, May 15 (10:00-11:00 PM ET/PT) on the CBS Television Network.

Police determined that the Pettits were shot a total of seven times before their bedroom was set on fire as a cover. Brandon Pettit, then 25, was charged with the murders, along with a friend, Felix Valverde.

"Is there any physical evidence that ties your brother to the murder?" Moriarty asks Lauren Pettit.

"No," Pettit replies.

Police and prosecutors maintain Brandon paid Felix to kill his parents because he wanted their money. Prosecutors pointed to promises Brandon made shortly before the murders to Sarah Wilson, a woman he knew from high school. Wilson testified for the prosecution.

"He had mentioned that his parents were going to buy him a million-dollar home in Georgia. And he said that I can move in with him," Wilson says.

"I got a text out of nowhere saying, 'You're getting a boob job for Christmas, LOL,'" Wilson adds.

Police said Pettit's reaction to his parents' deaths seemed muted. His former defense attorney maintains he's been diagnosed with Asperger's, which is an autism spectrum disorder. "He doesn't act the same way as you or I might act," says attorney Martha Carlton-Magana.

"There is no DNA. There are no fingerprints. There's no blood," says Mary Fulginti, a former federal prosecutor and CBS News consultant. "But what you do have here is a litany of statements and actions ... that point to Brandon."

Felix Valverde pleaded not guilty and has yet to go on trial. Could Brandon Pettit have coordinated the murder of his parents or were his statements just harmless words?

48 HOURS' "A Sister's Fight for Her Brother" is produced by Stephanie Slifer. Michelle Fanucci and Gayane Keshishyan Mendez are the development producers. Emma Steele and Addison Briley are the associate producers. Atticus Brady, Marlon Disla and George Baluzy are the editors. Lourdes Aguiar is the senior producer. Nancy Kramer is the executive story editor. Judy Tygard is the executive producer.

Follow 48 HOURS on Twitter, Facebook and Instagram. Listen to podcasts at CBSAudio.