A capital murder charge has been officially filed against the man accused of killing 20 people in a mass shooting in El Paso.

The US border city's prosecutor said he would seek the death penalty against a 21-year-old called Patrick Wood Crusius.

The El Paso Times, a sister paper of The Herald, said the suspected shooter had been booked in to County Jail early Sunday morning on a charge of capital murder.

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Crusius was arrested Saturday in connection with what is the the eighth deadliest mass shooting in U.S. history - and the 250 in America this year alone.

He allegedly walked into a Walmart near Cielo Vista Mall at about 10:40 a.m. and fired a rifle at hundreds of customers and employees, according to El Paso Police Department officials. The shooting left 20 people dead and 26 injured.

Several law enforcement agencies respond to an active shooter Saturday at the Walmart at Cielo Vista Mall in El Paso.

READ MORE: El Paso shooting: 20 dead and more than two dozen injured

No bond has been set for Crusius, jail logs show.

Jail records list Crusius, who is from Allen, Texas, as being six feet tall, weighing about 220 pounds with brown eyes and hair.

A mugshot of Crusius has yet to be released.

Court records show that an attorney has been appointed for Crusius, although it does not state which El Paso lawyer was appointed to represent him.

Records do not show when or if a bond hearing will be held for Crusius.

El Paso police officers, Texas Department of Public Safety troopers and other law enforcement officials were still at the scene of the Walmart on early Sunday morning.

Law enforcement is expected to remain at the scene throughout Sunday as they continue their investigation into the shooting.