Police on high alert after ex-LAPD cop's alleged serial shootings Authorities across Southern California were on high alert Thursday morning as a massive manhunt was underway for an ex-Los Angeles police officer sought in connection with a double homicide and the shootings of three police officers, one of whom was killed. Local, state and federal authorities are involved in the search for Christoper Jordan Dorner, 33, who threatened "unconventional and asymmetrical warfare" against police in a manifesto posted on his Facebook page. Dorner also threatened more than two dozen people -- including police officials -- in his manifesto. Officers from around Southern California have been deployed to protect those people. In some cases, police said, those at risk have relocated for their safety. PHOTOS: Manhunt for ex-LAPD officer LAPD Chief Charlie Beck is expected to hold a news conference at 10 a.m. When asked if police felt they were under attack, Riverside Police Lt. Guy Toussaint said: "Based on the circumstances of the shooting, yes I do." Hours after authorities announced they were looking for Dorner in connection with a double homicide in Orange County, the search intensified after three police officers were shot in Riverside County and Dorner was identified as a possible suspect. Ex-LAPD cop tried to steal boat, flee to Mexico, authorities say Freeway signs urged motorists to call 911 if they saw the suspect's vehicle as officers patrolled the streets near one of the Riverside County crime scenes with rifles at the ready. Los Angeles was put on a citywide tactical alert and California Highway Patrol issued a "blue alert" for nine Southern California counties warning Dorner was considered "armed and extremely dangerous." The first shooting occurred about 1:30 a.m. Thursday in Corona, where two Los Angeles Police Department officers providing protection for someone mentioned in Dorner's manifesto, officials said. One officer suffered a graze wound to the head during a shootout and Dorner fled the scene, police said. A short time later, two Riverside officers were shot at the corner of Magnolia Avenue and Arlington Avenue in Riverside. Toussaint said the officers were sitting at a red light when they were ambushed. One was killed, the other was still in surgery Thursday morning. Ex-LAPD officer threatened to kill in online manifesto There was no indication the officers were "actively seeking Dorner," Toussaint said. "Our officers were stopped at an intersection at a red light when they were ambushed," he said. Because of the close proximity to the timeline, we believe there is a strong likelihood that former LAPD Officer Christopher Dorner was involved in our incident. In the online manifesto, Dorner specifically named the father of Monica Quan, the Cal State Fullerton assistant basketball coach who was found dead Sunday in Irvine along with her fiance, Keith Lawrence. In the manifesto, he complained that Randy Quan and others did not fairly represent him at the review hearing. The violence of action will be high .... As authorities swarmed the area, two officer-involved shootings occurred in Torrance after police came across vehicles they thought might be Dorner's. The first Torrance incident occurred about 5:20 a.m. in the 19500 block of Redbeam Avenue in Torrance, Lt. Devin Chase said. That incident involved Los Angeles police detectives from the Hollywood division, sources said. Two people were struck by gunfire and transported to an area hospital with unknown injuries, Chase said. No officers were injured. The second incident, which involved Torrance police officers, occurred at Flagler Lane and Beryl Street about 5:45 a.m. No injuries were reported in that incident. Chase said both incidents involved vehicles matching the description of the one sought in connection with Dorner. "Now it appears neither of them are directly related," Chase said. In both of them, officers believed they were at the time. Authorities said they believe Dorner attempted to steal a boat from an elderly man about 10:30 p.m. Wednesday at the Point Loma Yacht Club in San Diego, hours before the shootings in Riverside County. The boat owner reported being accosted by a burly man who tied him up, threatened him with a gun and said he wanted the boat to flee to Mexico. But while they were trying to get underway, a rope became entangled in the propeller and the boat was inoperable, authorities said. The suspect fled the scene and the boat owner was unharmed. About 2 a.m., a citizen reported finding property belonging to Dorner on a street near Lindbergh Field, not far from the scene of the attempted boat theft. The property included a briefcase and Dorner's LAPD badge. Riverside police 'ambushed' by shooter, official says Police shoot two in Torrance in search for ex-LAPD cop Andrew Blankstein, Kate Mather, Phil Willon and Tony Perry