A federal appeals court on Tuesday cleared the way for the father of Oscar Grant III to sue the formerBART police officer who shot and killed his 22-year-old son.

A three-judge panel of the U.S. 9thCircuit Court of Appeals unanimously upheld a trial judge’s decision to permit the suit by Grant’s father, Oscar Grant Jr., againstJohannes Mehserle, who shot Grant on the platform of BART's Fruitvale Station in Oakland in the early morning hours of New Year’s Day 2009.

Mehserle said he meant to fire his Taser and mistakenly used his gun. A Los Angeles jury convicted him of involuntary manslaughter, and he was sentenced to two years in prison.

Lawyers for Mehserle had urged the 9thCircuit to examine whether the relationship between Grant and his father was close enough to justify a civil rights lawsuit alleging loss of companionship.

But the court declined to determine the contours of the relationship, observing the facts were disputed.

“With no authority to support it, we decline Mehserle’s invitation to find, as a matter of law, that Grant and his father lacked a sufficiently strong father-son bond to support the father’s 14th Amendment claim,” the panel said.