The man accused of gunning down nearly two dozen Walmart shoppers in Texas has been open with authorities, willingly giving detectives answers about one of the worst mass murders in U.S. history, officials said Sunday.

While El Paso police chief Greg Allen declined to elaborate on what kind of statements are being made by alleged mass murderer Patrick Wood Crusius, the 21-year-old has apparently spoken freely.

“He was forthcoming with information,” Allen told reporters. “He basically didn’t hold anything back. Particular questions were asked and he responded in the way it needed to be answered.”

Prosecutors said Sunday they’ll seek capital punishment against Crusius, who was arrested shortly after he allegedly killed 20 and wounded 26 by opening fire at a Walmart, filled with customers stocking up on back-to-school goods.

“He is eligible for the death penalty, we will seek the death penalty,” El Paso District Attorney Jaime Esparza told reporters. “The loss of life is so great we have never seen anything like this in our community.”

Moments later, U.S. Attorney for the Western District of Texas John Bash said his federal prosecutors are investigating Crusius “with a view towards bringing federal hate crime charges … and federal fire arms charges which carry a penalty of death.”

“We are also treating this as a domestic terrorism case,” Bash added. “This meets it and appears to be designed to intimidate a civilian population, to say the least. We’re treating it as a domestic terrorism case and we’re going to do what we do to terrorists in this country, which is to deliver swift and certain justice.”

Crusius, an Allen, Texas, resident, reportedly purchased the murder weapon legally, U.S. Rep. Veronica Escobar, told NBC El Paso affiliate KTSM on Sunday.

The alleged shooter was being held on capital murder charges, according to El Paso jail records.