Prosecutors said Sittler, a gang member, had gotten into a dispute with rival gang members. Three men, Giovanny Sanchez, now 37, his brother Erwin, 34, and Daniel Cruz, 33, were arrested and pleaded guilty to attempted murder.
Sittler recently died from pneumonia related to his original injuries, according to the Orange County Coroner's office. On Monday, prosecutors filed murder charges against the Sanchez brothers and Cruz.
Erwin Sanchez is currently serving a 20-year prison sentence for the attempted-murder conviction. Giovanny Sanchez served 11 years before being released and deported to Guatemala: prosecutors said they would seek his extradition to stand trial in California. Daniel Cruz served nine years and was released but was later convicted of armed robbery and is now serving a 23-year prison sentence.
Prosecutors say Erwin Sanchez fired the gun, and could face 38 years to life in prison if convicted of murder; his brother and Cruz could face 29 years to life.
The Associated Press contributed to this report.