Investigators believe Amber True, 29, and her boyfriend, Michael Guiterrez, 26, decided to target the Sonoma house after learning about the deaths in media reports.
"There is no indication at all to suggest they knew the family whatsoever and no connection to Sonoma," Sonoma Police Chief Bret Sackett said Wednesday. "Our speculation is they targeted the house because the accident was covered in newspapers, on television and the Internet."
Johnathan Maloney, his wife Susan and the couple's two young children were killed Saturday when a speeding Mini Cooper ran a red light and plowed into their minivan in southern Sonoma County.
The driver of the Mini Cooper, 19-year-old Steven Culbertson, also died of injuries.
Three days later, burglars ransacked the Maloneys' three-bedroom Sonoma house, taking jewelry, electronics and the family's 2006 silver Nissan 350z, police said.
True was arrested Tuesday afternoon after a San Mateo County Sheriff's deputy found her with a credit card belonging to Susan Maloney during a traffic stop. Detectives later found Guiterrez driving the stolen, and a search of his home found more property belonging to the family, police said.
Sackett said relatives still are trying to determine what was stolen.
"It's been very emotional for them," the chief said. "It's hard to fathom that they have to do through this in addition to dealing with their loss."
True and Guiterrez are being held on suspicion of burglary and vehicle theft.