California authorities are searching for a man who killed a small-town police officer the day after Christmas, a manhunt that prompted a tweet on Thursday from President Donald Trump.

Stanislaus County Sheriff Adam Christianson said Thursday they have identified the suspect who fatally shot Newman Police Department Cpl. Ronil Singh during a traffic stop, saying the man is living illegally in the United States but not naming him.

"We will relentlessly continue to hunt our suspect down and bring him to justice so that ... we can bring closure onto this community and this police department," Christianson said. “This suspect is in our country illegally. He doesn’t belong here. He is a criminal."

On Twitter, Trump connected the "full scale manhunt going on in California for an illegal immigrant accused of shooting and killing a police officer" to his call for a crackdown on border security as a partial government shutdown over funding for a wall along the U.S.-Mexico border stretched into its fifth day.

"Time to get tough on Border Security," Trump tweeted. "Build the Wall!"

Choking up about the killing of one of his department's 12 members, Newman Police Chief Randy Richardson pleaded for help in the search.

“He loved being a police officer,” Richardson said, shaking as tears welled in his eyes. “He loved being a husband. He loved being a father."

“My department is hurting. We’re struggling through this.”

Singh, 33, is the first Newman officer to die in the line of duty, Christianson said. Born in Fiji, Christianson said Singh immigrated to the U.S. to pursue a career in public service. Singh, who joined the Newman police force in 2011, is survived by his wife and 5-month-old son.

"He will never see his son walk," Richardson said. "He doesn't get to hold that little boy, hug his wife, say goodnight anymore because a coward took his life."

Early Wednesday morning, Singh stopped a pickup truck without a license plate as part of a drunken driving investigation in Newman, about 100 miles southeast of San Francisco. Singh fired back to try to defend himself, Christianson said, and later died at a local hospital. The suspect fled the scene but authorities later found the truck.

Authorities say surveillance photos from a nearby convenience store show the suspect, a heavyset man with short dark hair wearing a chain necklace, dark T-shirt and jacket.

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Police departments from San Francisco to Los Angeles have tweeted the suspect's picture, calling for the public's help and offering condolences.

"We want to see this face all over Twitter until he is caught — he is the suspect in the senseless killing of Newman Police Officer Ronil Singh," the Los Angeles Police Department tweeted. "You will be caught ..."

Donations to Singh's memorial fund can be made on the Stanislaus County Sworn Deputies Association's website.