SAN FRANCISCO (CNN) -- The gun used in the killing of a San Francisco woman in a case that gave new political prominence to the issue of illegal immigration belonged to a federal agent, a source with knowledge of the investigation told CNN.
Kate Steinle was shot to death on July 1 on one of San Francisco's busiest piers.
The San Francisco Chronicle reported the weapon was stolen in a car burglary in June, citing sources close to the investigation.
Some of the sources said the .40-caliber pistol was apparently not the agent's official gun.
Juan Francisco Lopez-Sanchez, the man accused in Steinle's killing, told CNN affiliate KGO-TV that he fired the weapon, but it was an accident.
In the interview, Lopez-Sanchez said he found the gun wrapped inside a T-shirt before it accidentally went off.
Politics of immigration
Lopez-Sanchez is an undocumented immigrant and a repeat felon who has been deported to Mexico five times, according to immigration officials.
The case has drawn the attention of presidential candidates and brought a renewed focus on U.S. immigration laws and the role local authorities should play in enforcing them.
The key question is whether San Francisco's policies set the stage for the shooting by putting a criminal on the streets instead of delivering him into the hands of federal authorities who could have deported him again.
Republican contender Donald Trump has blamed immigration policy for Steinle's death. Another Republican, Jeb Bush, agreed, saying such policies encourage crime.
In an interview Tuesday with CNN, Democratic presidential hopeful Hillary Clinton said San Francisco should have listened to the Department of Homeland Security and made a mistake when it didn't send Lopez-Sanchez packing.
"I have absolutely no support for a city that ignores the strong evidence that should be acted on. ... If it were a first-time traffic citation, if it were something minor, a misdemeanor, that's entirely different," she said. "This man had already been deported five times. And he should have been deported at the request of the federal government."
Immigration and Customs Enforcement said Lopez-Sanchez has seven felony convictions, four for drug offenses. His most recent deportation was in 2009.
On Tuesday, Lopez-Sanchez pleaded not guilty to murder and weapons charges. His bail was set at $5 million.
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