He asked them their religion but shot them no matter the answer. He even shot a woman in a wheelchair.
The description of the savagery that killed nine people at Umpqua Community College in Oregon on Thursday came from one of the survivors, a woman who was shot in the hand.
The mother of another survivor, Summer Smith, said the shooter spared her son so he could deliver a message to police but forced her son watch the murders.
"The shooter asked him to give the police something, and that if he did, he would live," Smith recalled.
Her son Mathew didn't at first understand what Chris Harper-Mercer meant. Mathew thought he was "standing up to die," his mother said.
Instead, she said, Harper-Mercer ordered Mathew "to sit in the back of the room ... and to watch what was going on."
Gunman issued orders
Tracy Heu told CNN's Sara Sidner in an exclusive interview
that she was sitting at the front of the classroom facing her teacher when the gunman entered with a shot.
"He just came in and shot towards the back of the wall and told everybody to get in the center of the room and on the ground," Heu said.
Harper-Mercer, 26, had guns and wore body armor, she said, and seemed determined to shoot. He didn't appear anxious or stressed, but rather "he seemed happy about it," Heu said.
A mother of three said she's relieved to be alive. She and two other people were the only ones able to walk out of the classroom. Everyone else was either too wounded or dead.
Harper-Mercer's victims ranged in age from 18 to 67
. Sarena Moore, 44, who was in a wheelchair, was shot to death after she got to the floor and Harper-Mercer ordered her to get back into her chair.
"She got off the chair, she went on the ground, and then he told her to get back on the chair," Heu said. "And then she tried to climb back on the chair, and then he shot her."
Moore's service dog survived, said Pastor Christian Martin of Grants Pass Seventh-Day Adventist Church, which Moore regularly attended before moving to be near the college in Roseburg.
Survivor singled out
Survivors have said the gunman gave an envelope to someone in the classroom, telling the student he would live if he gave it to police.
Smith told CNN that person was her 18-year-old son, Mathew. She said she didn't want to reveal his last name.
Smith said that after three people were shot and killed, the gunman paused and spotted her son. "Hey you, with the glasses," he called out.
"The shooter asked him to give the police something, and that if he did, he would live," Smith said.
"Mathew said at that point, he didn't quite get what the shooter said. He thought he was standing up to die, and that when the shooter gave him what he was told to give to police, he was then sent to sit in the back of the room ... and to watch what was going on."
Her son did as he was told, she said.
"Mathew said that he froze. He didn't make a single move. He was afraid to look away. That if he ... did anything to make the shooter notice him, that he would be shot. So he just sat there," Smith said.
"He's sitting there, watching the shooter execute people?" asked CNN's Dan Simon.
Mathew never saw the contents of the envelope but could feel a computer flash drive inside, his mother said. He gave it to police.
Law enforcement officials familiar with the investigation have told CNN the gunman handed his "writings" to a survivor, telling that person to give it to police, but they haven't elaborated on the form in which they were delivered.
Those officials say the writings indicate the shooter studied past mass shootings and identified with the perpetrators of those rampages. The shooter also expressed frustration at not having a girlfriend and being a virgin, the law enforcement officials say.
Survivor says religion not a factor
Relatives of two wounded victims have said the gunman asked his victims about their religion before he shot them.
One victim, Cheyeanne Fitzgerald, didn't answer and was shot in the back, her mother said. Another victim, Anastasia Boylan, told her father the gunman asked specifically whether they were Christians.
Heu also said the gunman asked about religion. But she said it didn't seem to matter, because he shot some people even before he asked.
"I don't think he was really targeting them," she said. "I honestly don't think he was targeting anybody. He just wanted to do it for fun. 'Cause he still shot every single one that he asked. So I don't think he was actually targeting a specific religion."
Covered in someone else's blood, expecting to die, Heu said she played dead. Her head was on the ground and she tried not to look up so the shooter wouldn't see she was still alive.
'She had a big heart'
Moore was an active member of the Grants Pass church for several years and continued to visit occasionally when in town to see one of her three sons, Martin said.
He said Moore, who was in her third semester studying business at the college, "had a big heart."
"Sarena was one who, when she got to know someone, they became a close friend, a good friend," Martin told CNN. "She easily made friends, she easily won hearts."
Sciatica was the reason she used a wheelchair, but it was for convenience and comfort and wasn't a necessity, he said.
Moore was also the caretaker for her boyfriend, and the church has helped make sure he will be taken care of, Martin said. The church has also set up a fund to assist the family financially.
Saturday's weekly service became a special tribute to Moore that included songs, prayer and a moment of silence.
"We drew attention to the legacy that we all believe Sarena has left, and that is she was passionate and devoted and a firm believer in the power of prayer," Martin said.
"She always gave God credit for the way in which he opened doors for her to enroll as a student. ... She always asked for prayer from many, many people, and so we were recalling the emphasis she always made on prayer."
As Seventh-Day Adventists, Martin said, they believe they will one day see Moore again.
"For us it's not goodbye forever, but 'see you then,' reunited together at the resurrection morning. So that's our blessed hope."
Gunman owned 14 firearms
Harper-Mercer was enrolled in the class he targeted Thursday -- an English class taught by one of his victims, Lawrence Levine, 67.
Also killed were Lucero Alcaraz, 19; Treven Taylor Anspach, 20; Rebecka Ann Carnes, 18; Quinn Glen Cooper, 18; Kim Saltmarsh Dietz, 59; Lucas Eibel, 18; and Justin Dale Johnson, 34.
Ages of Umpqua's students vary widely. Of its 13,600 students, the average age was 38 during the 2013-2014 school year.
The gunman died after a shootout with police, but the state medical examiner has determined his death was a suicide
, said Douglas County Sheriff John Hanlin.
Investigators have found 14 firearms connected to the shooter, authorities said. Five pistols and one rifle were found at the college and the others were at his apartment, Celinez Nunez of the Bureau of Alcohol, Tobacco, Firearms and Explosives said.
The gunman's father, Ian Mercer
, says he was unaware his son had any firearms.