Police say it's unlikely anyone will ever know what led a mother to shoot her daughter, then shoot herself at their Stacy Court home in the early evening hours of May 7.
"Forensic evidence that we now have access to leads us to conclude that Amy shot and killed her daughter, Ainsley, then killed herself," Bretzing said in a Friday news conference. "We don't know what her state of mind was or what she was going through."
Forensic evidence awaited by police included an analysis of the handgun used in the double shooting, he said.
"Testing of the gun, the types of wounds, the location and nature of those wounds Â… the firearms, specifically testing those," Bretzing said.
Christopher Burton, Amy Burton-Freeman's husband, "was never a suspect," Bretzing said.
"He's been cooperative throughout the entire investigation," he said. "At this point there's no evidence anybody else was involved."
Police and the FBI were called by Burton-Freeman about a month before the shootings. She suspected her daughter had been in communication with an older man over the computer; the investigation turned up a 16-year-old boy in Kentucky.
Bretzing said FBI agents in Kentucky re-interviewed the boy and determined he was not involved.
Two handguns were recovered at the scene of the shootings. They'd been purchased out of state and were never registered in California, but Bretzing said failure to register them is not a crime.
Bretzing said the long wait to release information had to do with the backlog of cases at the county crime lab.
"We were working very closely with the Alameda County Crime Lab. They're very busy -- this isn't the only homicide they're working on in the county. Really, it has to do with the availability of their equipment and their ability to process our evidence."
There have been 63 homicides in Oakland this year alone.
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