MES, Iowa — An officer was justified in using deadly force this weekduring a high-speed chase that ended with gunfire on the Iowa StateUniversity campus, authorities announced Thursday.In a letteroutlining his findings, Story County Attorney Stephen Holmes said thesuspect — identified as Tyler Comstock, 19, of Boone — acted with"reckless disregard for the safety of all who were in his path" as hedrove a stolen truck through red lights and onto campus at speedsnearing 70 mph.Related Article:Iowa police forced to shoot raging driver on college campusComstockendangered the lives of officers, motorists and pedestrians in a "heartstopping event" that lasted under four minutes, according to Holmes'letter.Ames police officer Adam McPherson and other officersinvolved that morning "acted responsibly" after being placed "in animpossible situation," Holmes said."Had the officers not exitedtheir vehicles to confront Comstock," he said, "we have only speculationas to where the matter would have gone and what might have happened."Thedeadly pursuit began at 10:17 a.m. Monday when Ames police received areport of a stolen vehicle from a man who said his son had become upsetand taken his pickup truck and trailer. According to a dispatchrecording, the father and son were working together."The son got mad at his dad and took off with the truck," the dispatcher reported.McPhersonwas the first to pursue the truck after spotting it at Grand Avenue andSouth 4th Street in Ames. He attempted a traffic stop, but Comstockinstead sped up and at one point reversed and rammed McPherson's patrolcar, according to authorities.During the pursuit, Comstock'struck spilled debris onto the road, nearly hit other motorists andendangered pedestrians before driving onto an ISU campus lawn. McPhersonand ISU police officer Tony Atilanto attempted to disable Comstock'struck by ramming it, according to Holmes' report.When thatfailed, and with both patrol vehicles disabled, the officers exitedtheir cars and McPherson fired seven times at the "back of the cab ofthe truck at the driver," according to Holmes. Comstock was hit twice --once in the head and once in the chest, according to an autopsy report.The officers had "every reason" to fear for their safety and the safety of others, Holmes said."Comstockgave no sign to either officer that he was going to cease the car chaseand end the threat he posed," according to Holmes' letter.And, Holmes added, the pursuing officers had little time to react."Itbecomes a very precarious exercise to attempt to pick apart splitsecond decisions," Holmes wrote. "Much deference has to be given whenquestioning an officer's presence of mind and judgment in a lifethreatening situation."Ames police Cmdr. Geoff Huff said theofficers pursuing Comstock "proceeded with care," reducing their speedsthrough intersections and backing off when supervisors suggested doingso."At the point when a supervisor made the comment to back off,the officer had already backed off and reduced his speed," he said.Officerscontinued following the truck with lights and sirens — but from adistance — as a warning to other drivers and pedestrians in the area,according to Huff."(Comstock) had not slowed down at all," Huff said. "We had."WhenMcPherson fired his gun, according to Huff, he was firing at Comstockin an attempt to "stop the threat." Huff said officers don't try toshoot out tires or at a vehicle engine."That doesn't work," Huff said. "You can still drive a car on flat tires. I've seen it many times."Comstockwas taken to Mary Greeley Medical Center, where he was pronounced dead.Huff said Comstock did not have any weapons with him in the truck.DuringThursday's news conference, authorities played two dashboard cameravideos. Both showed the stolen truck that Comstock was driving speedingthrough town and intersections — at one point backing up into thepursuing officer's squad car.Supervisors, during the incident,advised McPherson to "back off," according to a dispatch recording fromthe incident. Footage from McPherson's dashboard camera indicates he didslow down, losing sight of him at one point.