A US police officer lied when he said he was shot in the shoulder while standing in a police station car park last week and will face a criminal investigation.

Key points: Police officer Angel Reinosa told investigators that his bulletproof vest had saved his life after being shot at in the Lancaster station car park

Police officer Angel Reinosa told investigators that his bulletproof vest had saved his life after being shot at in the Lancaster station car park But no bullets were recovered at the scene and he had "no visible injuries"

But no bullets were recovered at the scene and he had "no visible injuries" The 21-year-old officer had been with the LA County Sheriff's Department for a year

"The reported sniper assault was fabricated" by Deputy Angel Reinosa, the Los Angeles County's Assistant Sheriff, Robin Limon, said at a news conference.

Mr Reinosa, 21, made a frantic radio call on Wednesday (local time) claiming he had been shot by someone in a nearby building as he walked to his car outside the Lancaster station, prompting a huge police response.

Officers set up a perimeter and SWAT officers went door-to-door inside a sprawling building complex to search for the shooter.

At the time, investigators believed Mr Reinosa's bulletproof vest saved his life but that a bullet grazed him.

Officers launched a widespread search for the sniper after Deputy Angel Reinosa made the frantic call last week. ( Supplied: ABC7 )

A department statement the next day said a single round hit the top of Mr Reinosa's shoulder, damaging his uniform shirt but failing to penetrate his flesh.

But no bullets were recovered from the scene and detectives saw "no visible injuries," Captain Kent Wegener said.

Much of the young deputy's statement "was self-serving and didn't make a whole lot of sense," Captain Wegener said.

"There were many things that didn't add up."

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Mr Reinosa eventually admitted making up the story and using a knife to cut the two holes in his shirt, Captain Wegener said.

Officer could face charges

The officer has been relieved of his duties and could face charges for filing a false report about a crime, officials said. He did not explain his motive for the fabrication, Captain Wegener said.

Mr Reinosa had been with the LA County Sheriff's Department for a year and joined the Lancaster station in May for patrol training.

Lancaster Mayor R Rex Parris told the Los Angeles Times on Sunday he had been informed by sheriff officials that Mr Reinosa had been struggling in his first year in the field.

"He was not advancing through the training program at an adequate pace," Mr Parris told the newspaper. "There had been a lot of attention on him."

Mr Parris declined to elaborate further on Mr Reinosa's performance but said the officer was scheduled to be transferred from the Lancaster station and speculated that he had been unhappy about the pending move.

The Mayor had visited Mr Reinosa in the hospital and then gave a press conference on the incident on Wednesday night detailing the ongoing investigation and said he was "embarrassed" after learning that the whole ordeal was a hoax.

"At the same time, I'm grateful we don't have a sniper running around," the Mayor told the newspaper.

"And I'm really proud of how the Sheriff's Department handled it. There was no attempt to cover it up."

Mr Reinosa's colleagues at the station released a statement saying they were "angry, embarrassed, furious, unbelievable and ashamed".

"Our deputies responded to a cry for help and did exactly what they have been trained to do to protect our civilian staff, residents and community," a department statement said.

"Our community and other first responder partners worked side by side with us to move quickly, effectively and efficiently. There is no shame in that."

The statement concluded: "The actions of one individual are not indicative of who Lancaster Sheriff's Station Deputies are."

AP