Ronald Jackson Jr., 20, was initially booked on suspicion of armed robbery and homicide in connection to the slaying of James Williams, 36, early Saturday at a Chevron station in Antioch, police said Wednesday.Antioch detectives submitted their findings to the Contra Costa County district attorney's office, and prosecutors "elected to charge Jackson with robbery, possession of stolen property, and a firearm enhancement, but declined to charge him with murder," police said in a statement.Jackson has been charged with second-degree robbery, a special allegation of using a firearm in that crime and receiving stolen property worth more than $950 — crimes that could land him behind bars for as long as 15 years — but not homicide.Because Jackson was wounded outside the Chevron, a legal expert says the suspect could have argued he was leaving the scene and had a legal right to protect himself.Williams' death will play a key role in seeking maximum punishment, according to Becton, even though Jackson won't be prosecuted for the clerk's slaying."