The sentencing hearing before U.S. District Judge David Guaderrama in El Paso could last several days given that every wounded survivor and families of the dead will be afforded the chance to testify.

The shooter, Patrick Crusius, 24, who admitted to targeting Hispanics, pleaded guilty in February to 90 counts including 23 counts of hate crime resulting in death under a plea agreement in which he agreed to 90 consecutive life sentences in order to avoid the federal death penalty.

Even with that agreement, the judge must conduct a sentencing hearing, at which every victim will have a chance to address the court with Crusius present.

The shooter also faces prosecution from the state of Texas that could result in the death penalty.

Gasps and cries could be heard from the packed gallery as Crusius entered the courtroom, according to multiple media reports from journalists witnessing the hearing.

The shooter, wearing a blue prison jumpsuit, glasses and shaggy long hair, showed no emotion and avoided looking at victims, reporters said.

"The killer the whole time showed very little emotion. He did not look over at any of the victims or the families," former El Paso Mayor Dee Margo, who was in office at the time of the massacre, told reporters during a recess in the proceedings.

Among the surviving relatives at Wednesday's hearing was Paul Jamrowski, the father of Jordan Anchondo, who was shot and killed along with her husband, Andre Anchondo, while protecting their baby Paul.

"We try to deal with it as every other family has, which is continue to go on with your life," Jamrowski told reporters in video published by KTSM television.

Just before the massacre, which was carried out with a Romanian derivative of the AK-47 and hollow-point ammunition, the shooter posted on the internet a manifesto that declared, "This attack is a response to the Hispanic invasion of Texas."

The shooter's attorney, Joe Spencer, did not respond to requests for comment on the hearing. At the time of the guilty plea in February, Spencer told reporters, "There are no winners in this case. He's going to be serving 90 consecutive life sentences."

(Reporting by Daniel Trotta in Carlsbad, California; Editing by Matthew Lewis)

By Daniel Trotta