The prosecution had asked for a second-degree murder conviction, which carries a maximum prison term of 15 years to life. But the jury convicted former transit officer Johannes Mehserle, 28, on the lesser charge after he claimed he had mistakenly pulled out a gun instead of his Taser.
Mehserle faces a maximum sentence of up to 14 years, including two to four years for involuntary manslaughter, and up to 10 years for use of a firearm while committing the crime. Sentencing is set for August.
Federal officials said they would review the killing of 22-year-old Oscar Grant to determine if the shooting warrants prosecution at the federal level, The Associated Press reported.
The protests of Thursday's verdict started peacefully, with about 500 people marching through downtown, but overnight turned into riots. The protesters, described by the San Francisco Chronicle as racially diverse, faced off with police, set fire to trash cans and sprayed walls with graffiti.
"This city is not the wild, wild West," Oakland's Police Chief Anthony Batts said. "This city will not tolerate this sort of activity."
Police arrested 83 people on charges of vandalism and assaulting a police officer, the Oakland Tribune reported, and reinforcements from other cities were called in. By later this morning, however, the city was reported to be calm.
At Mehserle's trial, which was moved to Los Angeles after rioting broke out on the day of the shooting, Jan. 1, 2009, the prosecution said the officer became angry when Grant tried to resist arrest.
During a videotaped confrontation, Grant was forced to lay facedown on a Bay Area Rapid Transit train platform, and Mehserle pulled out his gun and shot Grant in the back. But the jury found that Mehserle hadn't intended to kill Grant, although his behavior was criminally negligent. The jury included seven whites, three Latinos and one member listed as Asian-Pacific. One declined to provided a race.
Grant's grandfather, an Oakland resident, joined the protesters and told them not "to dishonor his grandson" by acting violently, the Tribune reported.
After the jury's finding, Grant's mother, Wanda Johnson, vehemently denounced the verdict.
"My son was murdered! He was murdered! He was murdered!'' she shouted outside the Los Angeles courtroom, the AP said.




