Last week, police arrested a man for opening fire at an Interstate 80 state rest stop, as well as a Pilot truck stop, in Atalissa, Iowa. Now, police have released a motive behind the shooting — the suspect wanted to harm semi truck drivers.

The shooter was identified as Illinois-resident Charles S. Johnston, a Psychology professor at Harper College in Palatine, Illinois, where he had been employed since 1996.

New court documents reveal the motive behind the shooting, and the chain of events that took place.

On January 11th, Johnston first opened fire at the Interstate 80 rest stop near mile marker 267 in Lime City, Iowa, then drove his black Volkswagen west, to the Pilot Travel Center in Atalissa.

As he was pulling into the Pilot, Johnston pointed a hand gun at a semi truck that was pulling out of the truck stop. Johnston fired multiple rounds at the semi driver, who swerved into Johnston’s black Volkswagen, wedging it underneath his trailer. Johnston then fired several more rounds into the door of the semi truck.

As Johnston was targeting the semi truck driver, police arrived at the scene and ordered Johnston to leave his vehicle. After a standoff that lasted for several minutes, Johnston finally submitted to police and was taken into custody.

Shortly after being taken into custody, Johnston told police the motive behind his attack.

Police say Johnston was “enraged or obsessed over a family member that was killed in an accident with a semi and that the motive behind his actions was to harm a truck driver or truck drivers in retaliation.”

Although the shootings occurred at two busy locations, no one was struck by the gunfire and there were no reported injuries.

According to local news source Quad-City Times, police found marijuana, a prescription pill bottle that contained pills that did not match the description, a pipe, and a jar of “Explosion Pre-workout” powdered-drink mix, inside Johnston’s vehicle.

Johnston’s employer, Harper College, says he was “absent without approved leave” and has been barred from returning to the school. The school also said they will cooperate with the police investigation.

Johnston has been charged with attempted murder and assault on a peace officer with a dangerous weapon, both felonies. He is currently being held in Cedar County, Iowa, on a cash-only bond of $1 million.

His arraignment is scheduled for March 2nd.

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