A manhunt has been launched after an illegal immigrant gunman shot dead a California police officer during a traffic stop.
The suspect had been stopped for possible drink driving when he shot the officer, Ronil Singh.
Donald Trump said the incident showed why his proposed wall on the US-Mexico border needed to be built.
Mr Trump said: "There is right now a full scale manhunt going on in California for an illegal immigrant accused of shooting and killing a police officer during a traffic stop. Time to get tough on Border Security. Build the Wall!"
There is right now a full scale manhunt going on in California for an illegal immigrant accused of shooting and killing a police officer during a traffic stop. Time to get tough on Border Security. Build the Wall!
— Donald J. Trump (@realDonaldTrump) December 27, 2018
The US government is currently partially shut down because Democrats have refused to grant Mr Trump billions of dollars in funding for the border wall.
Stanislaus County Sheriff Adam Christianson in California said authorities have identified, but won’t yet name the illegal immigrant suspect.
They believed he was still in the area, around 100 miles southeast of San Francisco, and was armed and dangerous.
Sheriff Christianson said: "This suspect is in our country illegally. He doesn’t belong here. He is a criminal.
"The sheriff’s office will spare no expense in hunting down this criminal."
Fighting back tears the local police chief Randy Richardson said Mr Singh, 33, originally from Fiji, had a newborn son, and was an "American patriot".
The police chief said: "He came to America with one purpose, and that was to serve this country.
"Please help us find this coward. We need closure, his family needs closure.
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"Please remember the man. Yes, he was a police officer, but he was a human being. His five-month old he will never hear talk, he will never see his son walk because a coward took his life."
Mr Singh stopped the attacker in Newman, a town of about 10,000 people, on Wednesday as part of a drunken driving investigation and fired back to try to defend himself.
Police were looking for a man seen in surveillance photographs at a nearby shop shortly before Mr Singh was killed.
Mr Singh was shot a few minutes after radioing that he was pulling over a grey pickup truck that had no licence plate.
A truck believed to have been the one stopped by Mr Singh was later found in a garage in a mobile home park about four miles from the shooting.