"As far as I can tell, there were about five people on that list," says Canton Police Chief Mike Echols.
The names on the list haven't been made public, but five people were taken into protective custody until the incident was over, McNamara says.
Police believe the suspect acted alone, McNamara adds.
The man had been barred from the school after several earlier confrontations, including "shoving and verbally abusing" coaches, authorities said.
Jeffrey Doyle Robertson, 45, went to the school just after classes started Thursday and shot coach Gary Joe Kinne, apparently with a .45-caliber pistol, police said.
The coach, who also is the school's athletic director, was airlifted to a hospital in nearby Tyler, and a family spokesman said he was in critical condition.
Robertson, who has a tattoo on his arm of cartoon character Yosemite Sam brandishing two guns with the words "Born to Raise Hell," was later found in the woods with self-inflicted wounds, including cuts to his wrists and thigh, authorities said. He had two guns and a pocketknife with him, Canton Police Chief Mike Echols said.
Robertson was scheduled to be arraigned Friday morning.
McNamara says the suspect had a reputation as a hothead, and had been involved in several angry confrontations over the alleged teasing of his son by other students.
Echols said Robertson had been barred from Canton High and told not to attend football games after the confrontations, including "shoving and verbally abusing" coaches at the annual football picnic.
Police were investigating a possible motive. On Wednesday, Robertson's son, Baron, had apparently been banned from playing all school athletics, said Steve Smith Jr., a senior who was a defensive end and kicker on the team.
Smith's father described Robertson as "a very high-strung, hot-tempered individual" who threatened Smith Jr. last year, grabbing his shirt and pushing him up against a fence, over an on-field teasing. He said Baron Robertson, then a freshman, was walking off the field when some older students "razzed" him.
"This guy blew up," Steve Smith Sr. said. "He thought some kids were picking on his son. My son wasn't even the one who said anything. But he threatened to kill him," The Associated Press quotes Smith as saying.
"I told my son, you know, 'You lay low if you see this man around,' Smith Sr. told McNamara. "I said. 'He's a time bomb.' I felt that when I met the guy, just because of the things he said."
Smith Jr. told The Early Show co-anchor Julie Chen Friday that Robertson threatened that evening to "take my whole family's life, for something I didn't do."
Smith Sr. told Chen his son then called him and said, "Dad, please come to the stadium just as soon as you can. Some guy is threatening my life."
Smith Sr. said he complained to the school and police, but Robertson was never charged.
Echols and Canton school district Superintendent Larry Davis said they were unaware of any previous threats.
Some parents had been upset that Kinne had made his own son the starting quarterback as a freshman, Smith Sr. said. G.J. Kinne was the Associated Press 3A all-state honorable mention quarterback last season.
Rhonda Miller, a cousin of Robertson's wife, was among the relatives gathered outside the jail Thursday night to help support Robertson's wife and son.
Miller said she didn't want Robertson portrayed as "a lunatic" because he wasn't the only one frustrated with the school's athletic program.
"A lot of parents are upset. This is not a single incident, and if they don't take care of it, it could escalate," she said, declining to elaborate.
Robertson worked for six years for Dallas Plumbing Co., leaving in 2002 to start his own business with another man. Company President John Downs described Robertson as a good employee and a devoted father who enjoyed taking his son hunting and fishing.
The last time Downs saw Robertson was about six months ago, when Robertson had a broken leg, bruises and abrasions from a road-rage-related fight on the side of a highway, he said.
"The last conversation that I had with him was that he really needed to learn how to control his temper or he was going to get hurt worse than that," Downs said.
Canton is a town of about 3,500 some 60 miles east of Dallas, and is known for holding a massive flea market each month.