The 17-year-old student who authorities said killed ten people when he opened fire in an art class in his Houston-area high school appeared to be disoriented on the morning after the attack, one of his lawyers said.
The teenager, identified by police as Dimitrios Pagourtzis, has been charged with capital murder.
He is being held without bail in Santa Fe, Texas, near where authorities said he opened fire shortly before 8am yesterday.
In addition to the nine students and one teacher killed, gunfire wounded ten people, with two of them in critical condition.
Nicholas Poehl, one of two lawyers hired by the suspect's parents to represent him, said he had spent a total of one hour with the teenager last night and this morning.
"He’s very emotional and weirdly non-emotional," the attorney said when asked to describe his client's state of mind.
"There are aspects of it he understands and there are aspects he doesn’t understand."
Asked if Pagourtzis has provided authorities with information about the shootings, Mr Poehl said: "Honestly because of his emotional state, I don’t have a lot on that."
Pagourtzis waived his right to remain silent and made a statement to authorities admitting to the shooting, according to an affidavit ahead of his arrest.
Yesterday morning, Santa Fe High School, southeast of Houston, became the scene of the fourth-deadliest mass shooting at a US public school in modern history.
The Texas shooting again stoked the nation's long-running debate over gun ownership, three months after a student-led gun control movement emerged from a mass shooting in Parkland, Florida, which left 17 teens and teachers dead.
The Pakistan Embassy in Washington DC identified one of the victims on Twitter as Sabika Sheikh, a Pakistani exchange student.
Her father said: "I kept calling her and sent her messages on WhatsApp. Never before had my daughter failed to reply.
"We are still in a state of denial. It is like a nightmare. She was coming back soon.
"There is a general impression that the life is safe and secure in America. But this is not the case."
Also killed was substitute teacher Ann Perkins, known to many as "Grandma Perkins," the Houston area CBS affiliate reported.
The brother-in-law of Cynthia Tisdale, a teacher's aide and mother of four, said on Facebook she was killed in the attack.
NFL star JJ Watt, who plays defensive end for the Houston Texans, said he will pay for the funerals of the deceased, local media reported.
Absolutely horrific.
— JJ Watt (@JJWatt) May 18, 2018
We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences
Classmates at the school of some 1,460 students described Pagourtzis as a quiet loner who played on the football team.
Yesterday, they said he wore a trench coat to school in Santa Fe, 50km southeast of Houston, on a day when temperatures topped 32C.
Texas Governor Greg Abbott said Pagourtzis obtained firearms from his father, who had likely acquired them legally, and also left behind explosive devices.
Abbott told reporters that Pagourtzis wanted to take his own life, citing the suspect's journals, but did not do so.
Pagourtzis was charged with capital murder and denied bail at a brief court hearing last nigth, where he appeared in handcuffs and wearing a green prison jumpsuit.
He spoke in a soft voice and said "Yes, sir" when asked if he wanted a court-appointed attorney, along with other questions.
Mr Poehl, the suspect's lawyer, said he expected a second hearing soon and would likely have more information about that on Monday. The discovery process by prosecutors would take a long time, he said.
Texas Attorney General Ken Paxton told CNN authorities were investigating whether anyone else helped in the attack.
Authorities have not disclosed how many explosive devices were found or if any of the deceased were killed or hurt by explosions. It is also unclear why the gunman targeted the art class.
Mr Abbott said investigators had seen a T-shirt on thes uspect's Facebook page that read "Born to Kill," and authorities were examining his journal. But there were no outward signs he had been planning an attack, he said.
