The Contra Costa County coroner’s office has identified two men who were killed in separate shootings in Richmond Tuesday night and early this morning.The violence started with a non-fatal shooting at about 11:10 p.m. in the 200 block of Sixth Street in Central Richmond, where police found a man suffering from gunshot wounds, police said. He was taken to a hospital and was reported to be in stable condition.A second shooting happened just 15 minutes later in the 800 block of Alamo Avenue in North Richmond, where officers found two people hit by gunfire, police said.One victim, a 17-year-old girl, was taken to the hospital in stable condition, but the second victim, 40-year-old Antoine Thomas, was pronounced dead at the scene. Thomas was a Richmond resident and was not far from his home when he was killed, a deputy coroner said.The third shooting happened at about 12:15 a.m. in the 4700 block of Hartnett Avenue in the city’s Upper South Side neighborhood, where responding officers found four gunshot victims. Two were hospitalized in serious condition, one was still in critical condition today and the fourth, 18-year-old Richmond resident Willie Brantley Jr., died at the scene, police said.No suspects have been identified and the motives for the shootings are still under investigation, Lt. Mark Gagan said today.Gagan said that although police so far haven’t been able to connect any of the shootings, they are concerned that they could prompt retaliatory violence.The Police Department has assigned additional officers to patrol the neighborhoods where the shootings happened, Gagan said.Those officers will be working around the clock to try to prevent further violence. They will also be taking a zero-tolerance approach to other types of crime, such as loitering, drinking in public and gambling, which can lead to more serious crimes, Gagan said.The Police Department is also offering $10,000 rewards for information leading to the arrest and conviction of the shooters and investigators are hoping that witnesses will come forward.Anyone with information is asked to call the Richmond police homicide section at (510) 620-6612 during business hours, or Sgt. Lori Curran at (510) 620-6647. The shootings bring the city’s homicide total to 24 so far this year. At this time last year there had been 17 homicides, Gagan said.