A former Marine has been identified as the gunman of a mass shooting on November 7 in the city of Thousand Oaks in Southern California in the US which left at least 13 people dead. A total of 25 people were injured in the shooting, according to authorities, Xinhua news agency reported. Ventura County Sheriff Geoff Dean on Thursday said the gunman was Ian David Long, 28, a Marine Corps veteran, who was described as "acting a little irrationally" when police were called to his home earlier this year to investigate a disturbance. He lived in Newbury Park, near Thousand Oaks. Dean said the gunman was armed with a Glock 21 - a brand of .45-caliber handgun. "The weapon was designed in California to hold a magazine of 10 rounds and one in the chamber, but he had an extended magazine on it," Dean said. Sheriff's officials said the shooter fatally shot himself after the massacre. He was found inside an office near the entrance of the venue. In the neighbourhood where Long lived, residents said they were well aware of his problems. Richard Berge, 77, was quoted by the US media as saying the former Marine had PTSD (post-traumatic stress disorder) and was known to kick in the walls of the home. Long lived with his mother, Berge said. A total of 25 other people were injured in the shooting, including 23 who self-transported themselves to hospitals, and two who were taken by ambulance, according to the Ventura County Fire Department. A procession was held Thursday morning for Deputy Sgt. Ron Helus killed while responding to the mass shooting. Helus' body was transported via motorcade from Los Robles Hospital to the Ventura County Medical Examiner's Office. People stood along the route with grief, paying salute to the officer. Helus was a 29-year veteran who was set to retire next year. He is survived by his wife and son. The motive of the shooter remains unknown. Authorities said hundreds of people were inside the bar when the gunfire rang out. No other victims have been identified by officials.