WALNUT CREEK -- A one-time Stanford University student who killed his former girlfriend and himself at her home last month built the gun he used from parts he ordered from the Internet, police said Tuesday. 
 
 Scott Bertics, 21, turned the homemade weapon on himself after shooting 19-year-old Clare Orton in the doorway of her family's home on Holton Court, off Homestead Avenue, around 6:50 a.m. on July 21. Orton was home for the summer during a break from classes at San Diego State. 
 
 Police quickly focused the investigation on where Bertics got the two guns found at the scene. Neither had a serial number, Walnut Creek police Lt. Lanny Edwards said. 
 
 Further investigation revealed that he obtained parts to make his own guns by ordering them online, Edwards said. 
 
 "Basically, anyone can buy parts," Edwards said. "These places sell the metal. They sell a trigger assembly. They sell handles and stocks. Essentially, you can buy 80 percent of a gun. That's what he did." 
 
 According to Edwards, everything Bertics did to assemble the gun was legal. Such parts to build a gun generally would run between $400 and $1,200, according to websites advertising the parts and Edwards' own estimates. 
 
 Bertics, like Orton, was majoring in engineering. 
 
 Police have not said Bertics' motive in showing up at the Ortons' door. He and Orton dated for a while but had not seen each other in that capacity since 2013, Edwards said. 
 
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 Small aspects of the crime still were being investigated, according to Edwards, but nothing has happened in the two weeks since the shooting to indicate anyone else was involved or that Bertics tipped off anyone to his plans. 
 
 "This should not be seen as something that can easily be done," Edwards said. "He knew what he was doing." 
 
 According to Stanford's website, Bertics was part of a team in 2013 who worked on a project called "Controlling Robot Dynamics with Spiking Neurons" and wrote a paper with other team members in 2014 titled, "Controlling Articulated Robots in Task-Space with Spiking Silicon Neurons." 
 
 He took a leave from Stanford after the fall 2014 quarter and didn't return. 
 
 Orton was an honors student at San Diego State, according to a school merit page. Her Facebook page indicated she belonged to the Society of Western Engineers at San Diego State, and that she was part of the Eco-Action Club while attending Las Lomas High School in Walnut Creek, where she graduated in 2014. 
 
 Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rderh. ||||| Walnut Creek murder-suicide suspect used “ghost guns,” police say 
 
 A 21-year-old Lafayette man who shot his former girlfriend to death at her Walnut Creek home before taking his own life used two untraceable “ghost guns” he built himself with mail-ordered parts, police said Tuesday. 
 
 Scott Bertics shot and killed Clare Orton, 19, at her home in Walnut Creek’s North Homestead neighborhood about 6:50 a.m. July 21, said Walnut Creek police Lt. Lanny Edwards. 
 
 An investigation determined that Bertics had secretly purchased various parts for the guns by mail and then built the weapons himself, Edwards said. 
 
 Police referred to the firearms as “ghost guns” because they contained no serial numbers. 
 
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 The homemade guns usually include unfinished lower receivers, the critical mechanism from which bullets are fired. Lower receivers normally require serial numbers, but incomplete ones can be bought as just simple pieces of metal. 
 
 There was no evidence that the retailers sold Bertics the gun parts illegally, Edwards said. 
 
 “There has been nothing in this investigation to suggest anyone else was involved or had any knowledge of Scott Bertics’ plans prior to the tragedy,” Edwards said. 
 
 Bertics, who had once dated the victim, was a 2012 graduate of Acalanes High School in Lafayette who went on to Stanford University. 
 
 Orton was a 2014 graduate of Las Lomas High School in Walnut Creek, where she was a cross-country and track athlete. She was studying environmental engineering at San Diego State University and made the dean’s list in the fall semester. 
 
 Bertics also ran cross-country and track in high school, then studied electrical engineering and computer sciences at Stanford. He took a leave of absence from the university after the fall 2014 semester, officials said. 
 
 In September 2014, Gov. Jerry Brown vetoed a bill that would have tightened laws on unregistered guns built with parts purchased online and delivered through the mail. 
 
 The bill — proposed by state Sen. Kevin de León, D-Los Angeles — would have banned the sale of gun parts unless they had serial numbers and required buyers to go through background checks. 
 
 At the time, De León warned that criminals, gang members and anyone else who wants to avoid background checks can get the parts through the mail and assemble their own guns. 
 
 In his veto message, Brown said, “I appreciate the author’s concerns about gun violence, but I can’t see how adding a serial number to a homemade gun would significantly advance public safety.” 
 
 Henry K. Lee is a San Francisco Chronicle staff writer. E-mail: hlee@sfchronicle.com Twitter: @henryklee
– 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.