The suspect in the Texas school shooting began his attack by firing a shotgun blast through an art classroom door, sending panicked students to the entryway to block him from getting inside, witnesses said Saturday.
Dmitrios Pagourtzis fired again through the wooden part of the door and fatally hit a student in the chest.
He then lingered for nearly 30 minutes in a warren of four rooms, killing seven more students and two teachers before exchanging gunfire with police and surrendering, officials said.
Abel San Miguel saw his friend Chris Stone killed at the door and got grazed in the stomach by another volley of shots. He and others survived by playing dead.
"We were on the ground, all piled up in random positions," he said.
Breanna Quintanilla was in art class when she heard the shots and someone say, "If you all move, I'm going to shoot you all."
The 17-year-old Pagourtzis walked in, pointed at one person and declared, "I'm going to kill you." Then he fired.
"He then said that if the rest of us moved, he was going to shoot us," Quintanilla said.
When Quintanilla tried to run out a back door, she realised Pagourtzis was aiming at her. He fired in her direction.
"He missed me," she said. "But it went ahead and ricocheted and hit me in my right leg."
She was treated at a hospital and spoke with a brown bandage wrapped around her wound.
"It was a very scary thing," Quintanilla said. "I was worried that I wasn't going to be able to make it back to my family."
In their first statement since the massacre, Pagourtzis' family said the bloodshed "seems incompatible with the boy we love."
"We are as shocked and confused as anyone else by these events that occurred," the statement said, offering prayers and condolences to the victims.
The family said it remained "mostly in the dark about the specifics" of the attack and that it shared "the public's hunger for answers as to why this happened."
Zach Wofford said he was in his agricultural shop class when he heard gunfire from the art classroom across the hall. He said substitute teacher Chris West went into the hall to investigate and pulled a fire alarm.
"He saved many people today," Wofford said of West.
The Houston branch of the FBI tweeted that 13 people were wounded in the attack, up from 10 previously. Hospitals reported treating 14 people with shooting-related injuries Friday, and the reason for the discrepancy still was not clear.
In addition to a shotgun and a handgun, Pagourtzis also had several kinds of homemade explosive devices, but they were not capable of detonating, said Galveston County Judge Mark Henry, the county's chief administrator.
Investigators found a group of carbon dioxide canisters taped together, and a pressure cooker with an alarm clock and nails inside. But the canisters had no detonation device, and the pressure cooker had no explosive material, Henry said.
"They were intended to look like IEDs, but they were totally non-functional," Henry said.
Authorities have offered no motive, but they said in a probable-cause affidavit that the suspect had admitted to carrying out the shooting.
The gunman told police that when he opened fire, he avoided shooting students he liked "so he could have his story told," the affidavit said.