03/10/2014 AT 05:45 PM EDT
Police are still searching for a reason why a 19-year-old man shot and killed his parents before trying to murder two of his siblings inside their luxury Southern California home last month.
Ashton Sachs is set to be arraigned on Monday for murder and attempted murder with premeditation and deliberation. He's accused of killing his parents, Bradford, 57, and Andra, 54, while they slept in their San Juan Capistrano mansion on Feb. 9. He then allegedly went into his 8-year-old brother's bedroom and shot him before firing the gun at his 17-year-old sister and fleeing to Seattle, where he's attending college.
"We're still working to find a motive," said Orange County Sheriff's Department detective Justin Montano, the Orange County Register
But his parents' money may be a factor. While police were still trying to identify a suspect two weeks after the killings, Ashton and his older brother, Myles, filed court papers asking to be named guardians of their three younger siblings (including the 8-year-old boy, who is now paralyzed). The court records show they also sought guardianship of the family's sizable estate, the Register
The Sachses, who divorced in 1999 but worked and lived together in their $3.7 million home, owned properties in California, Florida, Nevada and Mexico.
Detectives looking into the killings found no signs of forced entry
at the heavily secured home and interviewed Ashton and other family members early in the investigation. But following a lead earlier this week, they re-interviewed Ashton at the home of relatives in San Diego County and arrested him on Thursday.
"We feel confident he's our suspect," Montano said. "Right now, we believe he's our only suspect."