EL PASO, Texas — The shooting that killed 20 people at a crowded El Paso department store will be handled as a domestic terrorism case, federal authorities said Sunday as they weighed hate-crime charges against the suspected gunman that could carry the death penalty.

A local prosecutor announced that he would file capital murder charges, declaring that the alleged assailant had "lost the right to be among us."

The attack on Saturday was followed less than a day later by the shooting that claimed nine lives in Dayton. Together the two assaults wounded more than 50 people, some of them critically, and shocked even a nation that has grown accustomed to regular spasms of gun violence.

Investigators focused on whether the El Paso attack was a hate crime after the emergence of a racist, anti-immigrant screed that was posted online shortly beforehand. Detectives sought to determine if it was written by the man who was arrested. The border city has figured prominently in the immigration debate and is home to 680,000 people, most of them Latino.

Using a rifle, the El Paso gunman opened fire on shoppers during the busy back-to-school season.

The attack targeted a Walmart and did not spread to other nearby shopping areas, El Paso police Sgt. Robert Gomez said.

Most victims were inside the store. By Sunday evening, all bodies had been removed from the store and the parking lot, police said. They did not release names or ages, though some families announced that loved ones had been killed.

Despite initial reports of possible multiple gunmen, the man in custody was believed to be the only shooter, police said.

Law enforcement officials identified him as 21-year-old Patrick Crusius from Allen, a Dallas suburb which is a nearly 10-hour drive from El Paso.

The suspect's grandparents, Larry and Cynthia Brown, issued a statement Sunday evening. A family friend read the statement aloud outside the couple's home in Allen, KDFW reported.

The Browns said they were "devastated" by the shooting and were praying for the victims. The couple added that while Crusius' driver's license shows their Allen residence, he had moved out of the home six weeks ago. Crusius was living with his grandparents while he attended nearby Collin College.

Crusius was arrested without police firing any shots and was jailed without bond, authorities said. There was no immediate indication that he had an attorney.

Gomez said Crusius surrendered after being confronted by officers on a sidewalk close to the scene. Police did not know how many bullets were fired or why the attack stopped.

"We don't have information on what prompted him to stop firing," Gomez said.

El Paso Police Chief Greg Allen said the suspect was cooperative and "forthcoming with information."