The US Attorney for the Western District of Texas said that the mass shooting in El Paso, Texas is being treated as a case of domestic terrorism in a statement released Sunday. The gunman will possibly face the death penalty as the U.S. Justice Department is “seriously considering” to bring federal hate crime and firearm charges according to US Attorney John Bash.

Bash says that the shooting appears to meet the statutory definition of domestic terrorism. The El Paso shooting took place in a Walmart and left 20 people dead and 26 more were injured. The incident “appears to be designed to intimidate a civilian population, to say the least,” according to Bash.

“We’re going to do what we do to terrorists in this country, which is to deliver swift and certain justice,” the US Attorney added.

The suspected gunman was charged with capital murder on Sunday and is being detained on no bond according to El Paso Police Sgt. Robert Gomez. The suspect has been cooperating with investigators, Gomez said.

Authorities are now investigating a manifesto that the shooter allegedly posted on website 8chan prior to committing the killings Saturday, 10:30 a.m. local time.

The suspect is identified as a resident of Allen, Texas who goes by the name Patrick Crusius. The 21-year-old man was arrested in the Walmart parking lot, CNN reports. According to an official speaking to the news outlet, Crusius was inside a vehicle when he saw responding law enforcement units. He then got out of his vehicle and walked over to law enforcement unarmed.