Oakland , California ( CNN ) -- A former police officer convicted of involuntary manslaughter for killing an unarmed man in Oakland , California , apologized to the public and described his memories of the moments after the shooting in a handwritten letter obtained by CNN . In the letter , Johannes Mehserle said he was `` truly sorry '' for killing Oscar Grant . `` For now , and forever , I will live , breathe , sleep , and not sleep with the memory of Mr. Grant screaming 'you shot me ' and me putting my hands on the bullet wound thinking the pressure would help while I kept telling him 'you 'll be okay , ' '' Mehserle says in the letter . `` I tried to tell myself that maybe this shot would not be so serious , but I recall how sick I felt when Mr. Grant stopped talking , closed his eyes and seemed to change his breathing . '' Mehserle 's letter was dated July 4 , four days before a jury found him guilty of involuntary manslaughter for shooting 22-year-old Grant on an Oakland train platform on January 1 , 2009 . Mehserle , who was on duty as a Bay Area Rapid Transit police officer at the time of the incident , said at the trial that he intended to draw and fire his Taser rather than his gun , CNN affiliate KTVU reported . `` I have and will continue to live everyday of my life knowing that Mr. Grant should not have been shot , '' his letter said . `` No words can express how truly sorry I am . '' The involuntary manslaughter conviction usually carries a maximum four-year sentence , but some in Oakland expected a tougher penalty for the former police officer , and took to the streets in protest Thursday . Crowds broke the glass of a Foot Locker and other stores . Others threw sneakers out of the store as police wearing gas masks stormed the area . Outside the courtroom , Grant family members expressed outrage at the verdict . `` My son was murdered . He was murdered . He was murdered . My son was murdered , '' said Grant 's mother , Wanda Johnson . `` The system has let us down , but God will never ever let us down . '' Johnson and other speakers said African-Americans have been the victims of police abuse and a biased judicial system . She said Mehserle was n't found accountable . `` We could n't get even six hours of deliberations , '' said Johnson , who accused jurors of being unfair . Oakland police said there were 78 arrests during Thursday night 's protests on charges including failure to disperse , resisting arrest , burglary , vandalism and assaulting a police officer . Mehserle 's trial was moved from Alameda County to Los Angeles because of pre-trial publicity . Members of the jury , which included no African-Americans , said they were unanimous in their decision . Their finding indicates that Mehserle was criminally negligent . The shooting was captured on a bystander 's cell-phone video camera . The video , which showed Mehserle pulling his gun and fatally shooting Grant in the back as another officer knelt on the unarmed man , was widely circulated on the Internet and on news broadcasts , and it spurred several protests in and around Oakland . Mehserle resigned his position a few days after the incident and was later arrested in Nevada . His sentencing is set for August 6 . Involuntary manslaughter carries a maximum sentence of up to four years in prison under California law . But the judge could add an `` enhancement '' that could provide a longer sentence because a firearm was used .
Letter says he is `` truly sorry '' for shooting Foot Locker . Mehserle says Johannes Mehserle screamed `` you shot me '' while Mehserle tried to reassure him . Jury convicted Grant of involuntary manslaughter . Family , protesters expressed outrage at the verdict .