Correction: An earlier version of this article erred in stating the date the crash occurred. It happened on Sept. 26, 2014.

The driver of the semi-truck that crossed the highway median and struck a bus of North Central Texas College softball players leaving four dead took his own life Friday.

Man charged in deaths of 4 NCTC softball players committed suicide over the weekend. Russell Staley died from gunshot wound to head Friday.

— Darin Allred (@DASportsTX) January 30, 2017 Online Tarrant County Medical Examiner records show that Russell Staley, 55, of Saginaw died of a gunshot wound to the head. The ME lists the manner of death as suicide. 

Four of the NCTC students died in the Sept. 26, 2104 crash: Jaiden Pelton, 19, of Telephone; Brooke Deckard, 20, of Blue Ridge; Meagan Richardson, 19, of Wylie; and Katelynn Woodlee, 18, of Dodd City.

In its report in November 2015, the National Transportation Safety Board blamed Mr. Staley for the crash. The federal agency, which investigates transportation crashes and makes recommendations to other agencies on changes that would increase safety, said Mr. Staley was likely incapacitated from using synthetic cannabinoids.

Mr. Staley was set to stand trial on four counts of first degree manslaughter in Murray County, Oklahoma on March 8.

Following the crash, authorities found a pipe that contained the synthetic drug in the cab of his truck but a drug test of Mr. Staley was inconclusive. The drug, commonly know as K-2, is sold in a number of stores with a warning that it is not for human consumption, but many smoke it as a recreational drug.

“Synthetic cannabinoids are chemical compounds that are marketed as allegedly legal alternatives to marijuana; however, their effects can be considerably worse and they have been known to cause psychosis, seizures and nonresponsiveness,” says an NTSB news release at the time the agency released its report.

The report to the board says Mr. Staley told investigators he was reaching for a soft drink when his truck veered off the northbound lane of Interstate 35 near Davis, Oklahoma. The truck crossed a 100-foot median before entering the southbound lanes and hitting a charter bus carrying the softball team. The bus flipped onto its side and the truck continued off the highway and into a wooded area.

“The lack of any type of evasive steering or braking by the truck driver while traveling across the median for more than 10 seconds — and the full throttle following impact with the medium-size bus — are inconsistent with a fatigue-related crash,” the report says in its findings. “The truck driver’s lack of corrective actions following the roadway departure was due to incapacitation, likely from use of synthetic cannabinoids.”