Cops: Engineering Major Used 'Ghost Gun' to Kill Ex Police say it had no serial number and was built online By Michael Harthorne, Newser Staff Posted Aug 5, 2015 2:06 PM CDT 91 comments Comments Stock photo. (Shutterstock) (Newser) – A 21-year-old former Stanford student killed his 19-year-old ex-girlfriend and then himself with a "ghost gun," say police. That phrase refers to a firearm that has no serial number, and the two "ghost guns" found on the scene in Walnut Creek, Calif., were homemade firearms built with parts bought online, the San Francisco Chronicle reports. Police say Scott Bertics shot and killed Clare Orton on July 21 at her home; the 19-year-old was on summer break from San Diego State University, the Mercury News reports. There was no serial number on either gun found at the scene. (The Chronicle notes that lower receivers on homemade guns normally bear the numbers, though "incomplete ones can be bought as just simple pieces of metal.") Yesterday police revealed the firearms had been built by Bertics—an engineering major who took a leave of absence from Stanford in the fall—using parts he ordered off the Internet. A person "can buy 80% of a gun" online, says Lt. Lanny Edwards, who added there is no evidence Bertics did anything illegal to get the parts. The Chronicle points out that California Gov. Jerry Brown last year vetoed a bill that would have required any gun part sold online to have a serial number and background checks for anyone buying those parts, saying he didn't believe the bill would "significantly advance public safety." Police have so far not identified a motive in the killing of Orton; the two last dated in 2013, the Mercury News reports.