***********UPDATE*********
It appears this suspect had a pretty extensive criminal background.
Investigators say Mark Becker, 24, walked past about 20 students prior to 8 a.m. local time before firing at Thomas, who was supervising a summer weight-lifting session.
Police said Becker shot Thomas multiple times, including once at close-range to the head, then retreated from the red barn that serves as the weight room as the high school is being rebuilt. No other students were hurt.
Becker fled the scene, and was arrested shortly thereafter in the driveway of his parents' home and charged with first-degree murder. Bond was set at $1 million, and Becker is being held at Cerro Gordo County Jail in Mason City, about 40 miles northwest of Parkersburg. His next scheduled court appearance is July 2.
The motive, in the meantime, remains unclear.
"Motive is another one of those areas that, it's just to early to speculate on," said Dave Winker, of the Iowa Division of Criminal Investigation.
Butler County sheriff Jason Johnson said Becker did not have a gun permit, and investigators did not provide details on where the gun came from, only that "it was a gun he had access to," the Cedar Rapids Gazette reported.
Court records indicate Becker has been arrested for drunken driving, assault, possession of drug paraphernalia, and in January, he admitted to police to being a methamphetamine user.
Mark Becker was an offensive lineman on Thomas' team through 2003; Becker's father, Dale, was a captain of one of Thomas' squads in the 1970s.
"The whole church cares for both families. I don't know that there are any sides, but just trying to care for them," associate pastor Phillip Jensen told the Des Moines Register.
The evening of Saturday, June 20, Mark Becker embarked on an evening of violence. It started when he allegedly took a baseball bat to the Cedar Falls home of Dwight Rogers, one of whose sons graduated in the same class as Becker.
After slamming his car into the house's garage door, Becker led police on a high-speed chase that crossed three counties, ending in Parkersburg, when he hit a deer while traveling at about 90 mph, according to police.
He was admitted early Sunday to Covenant Medical Center in Waterloo -- the very hospital Thomas was flown to and pronounced dead Wednesday.
Cedar Falls police said they believed Becker would undergo a psychiatric evaluation at the hospital, and that their department would be notified when he was released so he could be charged in connection with the events at Rogers' house.
However, Becker was released from the hospital Tuesday, but police said they were never notified. Police would not say whether Becker left the medical facility on his own or with someone he knew.
"We're still investigating the exact sequence of events," Butler County Attorney Greg Lievens said, according to the Cedar Rapids Gazette.
According to Iowa newspaper reports, Becker was convicted of drunken driving in 2005. He also pleaded guilty to misdemeanor serious assault and fourth-degree criminal mischief in two separate incidents in November and December of 2008, and was fined, sentenced to 90 days in jail, and received a year of probation. However, all but four days of the jail sentence were suspended.
In January, Becker was arrested for possession of drug paraphernalia after a sheriff's deputy found him with a glass meth pipe and a digital scale during a traffic stop, according to court records.
Becker, who admitted to using meth, pleaded guilty and was fined, according to court records.
Information from The Associated Press was used in this report.
