The teenager accused of killing 10 people at a Texas high school exchanged "a lot of firepower" with police before he surrendered, a county official has said.
Dmitrios Pagourtzis, 17, is suspected of storming an art classroom on Friday armed with his father's legally owned shotgun and handgun.
No motive has been made public yet but authorities said the suspect had admitted to carrying out the attack.
The gunman told police he avoided students he liked "so he could have his story told".
He yelled "surprise" before shooting, according to Texas representative Michael McCaul.
Pagourtzis also had several kinds of homemade explosive devices, but they were not capable of detonating, said Mark Henry, the Galveston County judge.
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Investigators found a group of carbon dioxide canisters taped together. They also discovered a pressure cooker with an alarm clock and nails inside.
However, the canisters had no detonation device and the pressure cooker had no explosive material, Mr Henry said.
Pagourtzis played on the junior varsity football team and was a member of a dance squad with a local Greek Orthodox church.
Acquaintances described him as quiet and unassuming, adding that he was a keen video game player who often wore a black trench coat and black boots to school.
Although most of the dead have not been publicly identified, it is thought a substitute teacher and a foreign exchange student from Pakistan were among those killed.
Another 10 people were wounded, including a school police officer who was the first to confront the suspect. He was shot in the arm.
Hospitals reported treating a total of 14 people for injuries related to the shooting. Two were listed in a critical condition on Saturday.
Pagourtzis, who is thought to have no prior arrests or confrontations with law enforcement, made his first court appearance by video link from Galveston County jail on murder charges Friday.
A judge denied Pagourtzis bond and took his application for a court-appointed attorney.
The shooting happened in Santa Fe, a city of about 13,000 people roughly 30 miles (48 kilometers) southeast of Houston.
It was the nation's deadliest such attack since the Florida massacre that saw 17 die in February.
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It was also the deadliest assault in Texas since a man with a semi-automatic rifle attacked a rural church late last year, killing more than two dozen people.
Meanwhile, students have been let back inside Santa Fe High School to gather belongings they abandoned when the gunfire began.
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