Authorities will seek the death penalty for the El Paso mass murder and are treating the shooting — which took the lives of 20 at a Texas Walmart while wounding 26 others — as a “domestic terrorist case.”

“The state charge is capital murder, and so he is eligible for the death penalty,” El Paso County District Attorney Jaime Esparza said during a Sunday press conference. “We will seek the death penalty. The loss of life is so great, we certainly have never seen this in our community.”

Patrick Crusius allegedly opened fire in the crowded Walmart Saturday. Investigators are now more certain than before that a racist manifesto posted online in the hours before the shooting was penned by Crusius, federal officials said.

“We’re going down that road. It’s beginning to look more solidly like it is the case,” El Paso police chief Greg Allen said.

The feds, meanwhile, are also exploring hate-crimes and domestic terror charges that are federal death penalty eligible.

“I’ve been in close consultation with US Attorney General [William] Barr. We are conducting a methodical investigation with our partners, a careful investigation but with a view towards bringing federal hate crimes charges and federal firearms charges that carry a penalty of death. We are seriously considering those charges,” said US Attorney John Bash.

“We are treating it as a domestic terrorism case, and we’re gonna do what we do to terrorists in this country which is deliver swift and certain justice.”

Crusius, who was taken into custody after the shooting, has been cooperating with police, according to officials.

He was charged with capital murder and being held without bail Sunday.