A former transit police officer who fatally shot an unarmed man at an Oakland train station was convicted of involuntary manslaughter Thursday, capping a racially charged case that raised fears in the Bay Area of possible violence after the verdict.

Prosecutors accused the ex-officer of intentionally firing his handgun as he tried to handcuff Oscar J. Grant III on New Year’s Day 2009. Johannes Mehserle, 28, tearfully testified that the shooting was a tragic accident caused when he mistakenly grabbed his firearm instead of an electric Taser weapon during a struggle with Grant.

The shooting was captured on video by several witnesses. Mehserle, who is white, fired a single round into the back of Grant, who was black and was lying face-down on the station platform. Mehserle resigned a week after the shooting.

The killing provoked protests and violence in Oakland. The case, which has drawn comparisons to the videotaped beating of Rodney G. King that ultimately triggered riots in Los Angeles in 1992, was moved to Los Angeles for trial amid concern about the extensive media coverage of the slaying in the Bay Area.

Many civil rights activists considered the case a test of how the justice system treats police officers accused of abusing minorities. The trial also captured the attention of law enforcement officers who feared that a guilty verdict could raise the stakes for cops who make mistakes.

The shooting occurred soon after police responded to reports of a fight on a train stopped at the Fruitvale Station. Grant and four friends were detained by a different police officer who prosecutors said used excessive force against the men. Mehserle arrived on the platform after the men had been detained.

Alameda County Deputy Dist. Atty. David R. Stein rejected the idea that the shooting was a mistake, telling jurors that Mehserle’s holster was specially designed to prevent easy release of his firearm. The prosecutor contrasted the light, bright yellow Taser gun with the heavier black Sig Sauer handgun that Mehserle fired.

“He let his aggression dictate his conduct,” Stein told jurors.

The prosecutor urged jurors to find Mehserle guilty of second-degree murder, pointing out that the officer never told his colleagues that night that the shooting was an accident.

Prosecutors in Los Angeles have not won a murder conviction in a police shooting case since 1983.

Mehserle testified that he intended to use his Taser because he believed Grant, 22, might be reaching for a gun in his pants pocket. While the officer’s firearm was on his right side, the Taser was in a holster on the left side of his belt but angled so that it could be pulled out with his right hand.

Two people, including a friend of Grant’s, testified that they heard the officer say he intended to use his Taser shortly before the shooting. In at least six other instances, officers have said they made the same mistake of firing a handgun when they intended to use a Taser.

Numerous witnesses said Mehserle looked shocked after the gunshot. Defense attorney Michael L. Rains said video footage shows his client holding his head in his hands in despair.

“He’s sick to his stomach,” Rains told jurors, “because he has shot a man who did not deserve to be shot.”

jack.leonard@latimes.com