The man, identified by authorities as Gustavo Perez Arriaga, was arrested Friday after a manhunt that fueled tensions over illegal immigration when President Donald Trump tweeted about it.

On Wednesday, Perez Arriaga’s lawyer argued he was mentally incompetent and unable to stand trial, delaying the criminal proceedings, said John Goold, a spokesman for the Stanislaus County district attorney.

Perez Arriaga, who is in his 30s, is accused of shooting and killing Ronil Singh, a 33-year-old officer with the Newman Police Department, early on Dec. 26. Police said the shooting occurred after Singh pulled Perez Arriaga’s vehicle over because Singh suspected that Perez Arriaga was driving under the influence.

The gunman fled in his pickup truck, according to a statement from the sheriff’s department. Perez Arriaga was arrested two days later.

Sheriff Adam Christianson of Stanislaus County said at a news conference Friday that authorities believed Perez Arriaga was trying to escape to Mexico when he was arrested that day at a home in Lamont, California, about 10 miles outside Bakersfield.

The sheriff said Perez Arriaga had crossed the border from Mexico illegally “some time ago,” worked as a farm laborer and bragged on social media about being active in a street gang.

The sheriff said Perez Arriaga had previously been arrested twice on suspicion of drunken driving.

In the criminal complaint, Perez Arriaga was also identified by three other names. Goold said prosecutors were not certain of his real name, but on Wednesday at the County Court in Modesto, California, he identified himself to the judge as Paulo Virgen Mendoza.

Stephen Foley, the defendant’s lawyer, did not immediately respond to a request for comment Wednesday evening.

According to the criminal complaint, prosecutors requested that the murder charge be considered under “special circumstances,” meaning the maximum punishment could be the death penalty or life in prison without parole. Those special circumstances include killing a police officer or committing murder in an attempt to avoid a lawful arrest.

Trump tweeted about the case during the police’s manhunt — and the federal government shutdown prompted by his demands for a border wall with Mexico.

Singh was an immigrant from Fiji, officials said, and had worked for the Newman Police Department since 2011. He was married and had a 5-month-old son.

After spending Christmas morning with his family, he went on duty that night. His funeral was Wednesday.

At least seven people have been charged with being accessories to the crime. Police say they helped Perez Arriaga elude authorities. All have pleaded not guilty, according to local news reports.

This article originally appeared in The New York Times.