A Mexican man who touched off a fierce immigration debate over his role in the shooting death of a woman walking on a San Francisco pier is seeking to overturn his felony gun possession conviction. It was the only charge he was found guilty of after a jury acquitted him of murder.

Jose Inez Garcia-Zarate had been deported five times at the time of the shooting and was wanted for a sixth deportation proceeding.

Lawyers for Garcia-Zarate filed the expected appeal last week in state court. He contends he didn’t know a gun was in his hands because it was wrapped in a T-shirt when it fired and he dropped it almost immediately after picking it up. He argues in court papers that he can’t be convicted of illegal gun possession.

Garcia-Zarate was charged with murder and illegal gun possession for the fatal shooting of Kate Steinle in July 2015. Steinle was shot in the back was she walked with her father on a city pier crowded with tourists taking in the sights.

Garcia-Zarate had been recently released from jail after prosecutors dropped a 20-year-old marijuana possession charge. He had been transferred to San Francisco’s jail after serving nearly four years in federal prison for illegal re-entry into the United States.

The San Francisco sheriff released Garcia-Zarate from jail despite a request from federal immigration officials to detain him until they could pick him up for deportation proceedings. San Francisco’s so-called sanctuary city policy bars local law enforcement officials from cooperating with most federal immigration investigations.

The shooting and the city’s sanctuary policy turned into a major campaign issue in multiple national and local races across the country. President Donald Trump repeatedly referred to the shooting during his 2016 campaign to bolster his argument for tougher immigration policies and his opposition to sanctuary cities.

The gun used in the shooting belonged to a U.S. Bureau of Land Management ranger who reported it stolen from his car parked in San Francisco. A San Francisco jury in 2017 acquitted Garcia-Zarate of murder but found him guilty of illegal gun possession and he was sentenced to the time he spent in jail awaiting trial.

Trump called the verdict in a Tweet “disgraceful” and former U.S. Attorney General Jeff Sessions blamed San Francisco’s sanctuary city policy for Steinle’s death. The U.S. Attorney in San Francisco then filed federal charges of illegal gun possession and he was transferred to federal custody.

That case has been on hold pending the outcome of a closely watched U.S. Supreme Court case challenging federal prosecutors’ authority to duplicate state court charges in federal court. If the Supreme Court finds the practice unconstitutional double jeopardy, a federal judge said he would dismiss Garcia-Zarate’s federal gun case.