Trial has begun for a deputy U.S. marshal who fatally shot a Los Angeles man in an alley after a night of drinking.

Matthew Itkowitz's federal trial began Tuesday with jury selection. He has pleaded not guilty to civil rights violations and obstruction of justice

Prosecutors say Itkowitz and his wife were walking home from a bar in 2008 when they began fighting. Prosecutors say a stranger, 26-year-old Ryan Gonzalez, intervened when Itkowitz's "hysterical and crying" wife ran for help.

Itkowitz acknowledged shooting Gonzalez, citing self-defense. Gonzalez was shot five times.

Federal authorities charged Itkowitz after local prosecutors decided against it, saying they lacked evidence to prove it wasn't self-defense. Federal prosecutors argue Itkowitz was acting "under color of law," saying he identified himself as police before shooting Gonzalez.