The man charged in the El Paso Walmart mass shooting is on suicide watch, authorities say.

Patrick Crusius, charged with killing 22 and injuring 25 earlier this month was placed under close guard Monday on the recommendation of medical staff at the county jail, according to an El Paso County Sheriff's Office official.

The gunman, a 21-year-old white male from a Dallas-area neighborhood, has been in custody since Aug. 3 without bond shortly after the shooting, according to a police affidavit.

READ MORE: El Paso gunman confessed to targeting Mexicans, police say

The shooter was separated from other inmates and placed in a single jail cell at the Downtown jail, according to the sheriff's office. He has been in the jail under a capital murder charge since Aug. 4.

The U.S. Attorney's Office is also investigating the case with the possibility of filing federal hate crime and domestic terrorism charges against the shooter, according to John Bash, of the Western District of Texas.

The assailant allegedly confessed to the mass shooting to officers as he was surrendering, according to a police affidavit, and admitted to targeting Mexicans.

He left his home in suburban Dallas to drive about 10 hours with the intent to kill Hispanics, authorities believe. The shooter, who is white, laced his manifesto with anti-immigrant and racist rhetoric, saying he advocated a plan to divide the nation into territories by race.

Those killed ranged in age from 90 years old to a 15-year-old high school student.

It’s believed he used an AK-47-style gun to gun down people at the Walmart. He is believed to have posted an online manifesto referencing a weapon similar to the AK-variant semi-automatic rifle seen in surveillance video from the El Paso Walmart.

This story first appeared in the El Paso Times, one of The Herald's American sister papers