A massive manhunt was underway Thursday morning for an ex-Los Angeles Police Department officer suspected of shooting three police officers early Thursday, one fatally. He is also a suspect in the shooting of a couple in Irvine over the weekend.

The suspect is believed to have written an online manifesto on what authorities say is his Facebook page, threatening to harm police officials and their families, law enforcement sources said.

PHOTOS: Manhunt for ex-LAPD officer

The three shootings early Thursday morning occurred in Riverside County.

One LAPD officer was grazed in the Corona area, law enforcement sources said. Then sometime later, two Riverside Police Department officers were shot in Riverside. One of those officers died, sources said. That shooting occurred at Magnolia and Arlington avenues. The officers were taken to Riverside Community Hospital.

Officials warned that the suspect, Christopher Jordan Dorner, 33. is armed and dangerous. Law enforcement sources said police have placed security at the homes of LAPD officials named in the online documents and believe that Dorner has numerous weapons.

Hundreds of officers were swarming around the Riverside shooting scene looking for the gunman.

The California Highway Patrol issued a "blue alert" to law enforcement:

*THE SUSPECT IS CONSIDERED ARMED AND EXTREMELY DANGEROUS* A BLUE ALERT HAS BEEN ACTIVATED IN THE FOLLOWING COUNTIES: KERN, SANTA BARBARA, VENTURA, LOS ANGELES, SAN BERNARDINO, ORANGE, RIVERSIDE, SAN DIEGO, AND IMPERIAL. ON FEBRUARY 7, 2013, AT APPROXIMATELY 0122 HOURS, THE SUSPECT WAS INVOLVED IN MULTIPLE SHOOTINGS WITH MULTIPLE AGENCIES IN THE RIVERSIDE CHP AREA.



THE SUSPECT IS CHRISTOPHER JORDAN DORNER, A 33 YEAR OLD, BLACK MALE, 6 FEET TALL, 270 POUNDS, WITH BLACK HAIR, BROWN EYES, WITH AN UNKNOWN CLOTHING DESCRIPTION. THE SUSPECT WAS LAST SEEN DRIVING A 2005 BLUE OR GRAY NISSAN TITAN, WITH A CA LICENSE PLATE OF 8D83987 or 7X09131 - THE SUSPECT MAY BE SWTICHING BETWEEN THE TWO LICENSE PLATES.

THE VEHICLE ALSO HAS SKI RACKS ON ITS ROOF.

Irvine police Wednesday night named Dorner as the suspect in the double slaying in the parking lot of an upscale Irvine apartment complex Sunday.

In the online postings, Dorner specifically named the father of Monica Quan, the Cal State Fullerton assistant basketball coach who was found dead Sunday, along with her fiance, Keith Lawrence.

Her father, Randy Quan, a retired LAPD captain, was involved in the review process that ultimately led to Dorner's dismissal.

Ex-LAPD cop tried to steal boat, flee to Mexico, authorities say

A former U.S. Navy reservist, Dorner was fired in 2009 for allegedly making false statements about his training officer.