SAN FRANCISCO (CBS / AP) — A judge says he’s skeptical of a Mexican national’s claim that he’s a target of a vindictive federal prosecution because a San Francisco jury had acquitted him of murder in a case at the center of a heated national debate over immigration.

U.S. District Judge Vince Chhabria said Tuesday that Jose Ines Garcia-Zarate faces an uphill battle proving federal gun charges were brought solely because of politics.

READ MORE: Marin Brewing Company Shutting Down After 3 Decades Due To Pandemic Struggles

A San Francisco jury acquitted Garcia-Zarate of murder in the July 2015 shooting death of Kate Steinle on a San Francisco pier.

READ MORE: UPDATE: Suspect In Attempted Armed Carjacking Killed In Shootout With San Jose Police

He had been released from jail weeks earlier despite federal immigration request to detain him for deportation. San Francisco’s so-called sanctuary city policy bars local cooperation with federal deportation efforts.

Federal officials charged him with illegal gun possession five days later.

MORE NEWS: Queen Of The Valley Hospital Workers Stage Picket Over Pandemic Staffing, Pay Issues

© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.