Unexpected twist in deadly San Francisco shooting

Last Updated Jul 8, 2015 2:57 PM EDT

Accused gunman Juan Francisco Lopez-Sanchez has been at the center of a debate over a San Francisco policy that prohibits city employees from aiding immigration authorities with investigations or arrests unless it is required by law or there is an active arrest warrant. But now that a federal agent's gun was used in a murder, the policy debate is being eclipsed by this unexpected twist in the crime itself, reports CBS News correspondent John Blackstone.

Man deported 5 times charged in San Francisco killing

Over and over Tuesday, Lopez-Sanchez, an undocumented immigrant, told the judge he was "not guilty" in the shooting death of Kathryn Steinle. The 32-year-old was gunned down last week as she and her father strolled along San Francisco's waterfront. Sanchez contends he found the gun wrapped inside a T-shirt on the Pier, and it went off accidentally.

"This very well could be a completely accidental discharge of a firearm," defense attorney Matt Gonzalez said.

The U.S. Bureau of Land Management said Wednesday that a service weapon issued to one of its agents was used in the shooting. The agency is part of the Interior Department.

A law enforcement source told CBS News senior investigative producer Pat Milton that the weapon was reported stolen in a car burglary in San Francisco in June. A spokesman for the agency said the matter was under investigation, Milton reports.

Questions about the firearm were raised even before news of its use in the crime broke late Tuesday.

"Where did the gun come from? How many times was it fired? We don't have this information yet. But going forward, we will thoroughly investigate the case," San Francisco public defender Jeff Adachi said.

San Francisco under fire for "sanctuary" immigration policy

Sanchez has been at the center of a growing debate over "sanctuary cities" like San Francisco and Philadelphia. The Sheriff's Department released Sanchez from custody in April without telling federal authorities. They had asked to be notified when he was set free.

Presidential hopeful Hillary Clinton addressed the issue Tuesday.

"This man had already been deported five times. And he should have been deported at the request of the federal government," she said.

Prosecutors said the focus shouldn't be on the gun or immigration issues, but on the victim in the case.

"Today is about Kate," San Francisco District Attorney spokesman Alex Bastain said. "And it's about doing everything we can to bring this justice that this family rightfully deserves."

In a jailhouse TV interview Sunday, Lopez admitted killing Steinle, but his defense attorney says his client was dealing with a language barrier and didn't know what he was saying, leading to Tuesday's not guilty plea.

Sanchez remains in jail, with his bail set at $5 million.