A Los Angeles jury convicted former Bay Area Rapid Transit (BART) Officer Johannes Mehserle of manslaughter later Thursday for causing the death of Oscar Grant III, who he shot and killed Jan. 1, 2009, during an arrest.

The 28-year-old former transit officer shot the unarmed, face-down Grant, 22, at BART's Fruitville Station platform. Another officer held a knee on his back. The incident was captured on at least five cellphone cameras.

Mehserle faces a sentence of between two to four years for involuntary manslaughter , plus up to 10 years for using a gun, SF Gate.com reports. Judge Robert Perry could impose a minimum sentence of five years, and a maximum sentence of 14 years.

Fearing a tainted jury pool and possible violent protests , prosecutors chose Los Angeles as the venue for the racially tinged case. Anticipating possible rioting after the verdict, county offices in downtown Los Angeles were evacuated early Thursday afternoon.

Convicting an officer in a deadly force encounter is a tall order for prosecutors faced with the burden of proving the officer's intent, said Sandi Gibbons, public information officer with the Los Angeles County District Attorney's Office.

"In our society, police officers are given the right to use deadly force when the force directed against them is deadly," Gibbons told POLICE Magazine. "And police officers, when they come into a courtroom, are the cleanest-cut American guys."

During the trial, Mehserle and two colleagues involved in the incident—the three officers lost their jobs over the incident—testified about their role in the arrest. Mehserle, who wept on the witness stand , said he mistakenly pulled his SIG Sauer service pistol and shot Grant when he meant to use his TASER.

A police trainer testified that Mehserle was trained on the importance of not confusing the TASER with his duty weapon.

The last time an officer or deputy was convicted for murder or manslaughter in Los Angeles County was almost three decades ago. Los Angeles prosecutors obtained a second-degree murder conviction in 1983 of Los Angeles County Sherif's Deputy Robert Armstrong, who shot and injured a pregnant woman, whose fetus didn't survive. Armstrong had conducted an illegal raid on a suspected drug house.

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