Los Angeles police launched a full-scale manhunt on Thursday for a dismissed officer believed to have killed three people in the US state of California including another cop.
Christopher Jordan Dorner had posted a chilling online warning about "terminating" the life of a colleague he blamed for his dismissal, and threatening other police and their families.
The LA Police Department (LAPD) said it was increasing protection for a number of people named in an online manifesto by Dorner, a 33-year-old US Navy reservist who was described as "armed and extremely dangerous".
Dorner was already wanted over the suspected revenge killing on Sunday of a couple, Keith Lawrence and Monica Quan, who was the daughter of Randy Quan, a retired police officer he blamed for his firing.
Then he allegedly attacked two other officers overnight on Wednesday in Riverside, east of Los Angeles, killing one and injuring the other, triggering the full-scale manhunt.
Dorner posted a multi-page manifesto online Monday, saying he was not afraid to die because he had already died when he was dismissed in September 2008 for making false statements about his training officer.
"I never had the opportunity to have a family of my own, (so) I am terminating yours," he wrote to Randy Quan.
"Suppressing the truth will (lead) to deadly consequences for you and your family. There will be an element of surprise where you work, live, eat and sleep," he said, referring to Quan and several others.
An LAPD statement on Wednesday said it took the threats "very seriously" and promised "all measures possible to ensure the safety of our LAPD personnel, their families and the Los Angeles community".
An elite LAPD squad "will continue to do so until Dorner is apprehended and all threats have been abated," it added.
He is described as black, six feet tall and weighs 120kg. Anyone encountering Dorner should consider him "armed and extremely dangerous," it said.
LAPD chief Charlie Beck was due to give a press briefing at 10am (1800 GMT) on Thursday.