In the end, only the gunman - identified by police as 29-year-old Patrick Gray Sharp - was killed.
Sharp died after aTuesday morning. McKinney police Chief Doug Kowalski says it's unclear whether he was killed by an officer's bullet or one of his own.
It's also unclear what his motive was.
"He had a plan. He was activating his plan. He was heavily armed," Kowalski said. "He looked like he knew what he wanted to do. What we don't know is why he wanted to do it."
Sharp may have intended to lure people from the police station so that he could shoot at them from a field across the street where he had taken position, Kowalski said. He also may have intended to kill them by blowing up the trailer, he said.
The fire set off ammunition in the truck but failed to ignite the trailer, which was filled with wood chips, ammonium nitrate, gasoline and road flares, Kowalski said.
Investigators found an assault rifle, a shotgun and a handgun on Sharp. Kowalski said Sharp fired at least 100 rounds at the police station, and the chief counted at least 23 bullet strikes on the building.
The chief said Sharp was found dead after police fired an unknown number of rounds while pursuing him in a line of trees where Sharp had taken cover and into an open field near Collin College, which was on lockdown after the shooting.
Sharp's roommate, Eric McClellan, told The Associated Press by phone that he was on vacation outside Texas when he received calls from state troopers and his stepfather telling him what happened. He said he was "still in shock" and that there was nothing about Sharp that would lead him to believe he would try to attack police.
"He was fine and dandy when I left Texas two days ago, and, all of a sudden, I get a phone call," McClellan said. "There's nothing I can say. He was a great guy, a good friend."
McClellan said he was questioned about Sharp by police and couldn't provide them with much information.
He said he and Sharp kept guns in their residence because they like sports shooting.
"We're Texans," he said. "We have the right to bear arms."
McClellan said he was doing contract work for building wire manufacturer Encore Wire Corp. six years ago when he met Sharp, who was an employee of the company. They had been roommates for four years, he said.
Collin County records show Sharp and McClellan are co-owners of the home they shared near Anna, a town about 15 miles north of McKinney.
Authorities descended on the rural cluster of manufactured homes not long after news of the shooting broke, neighbors said. They were still there nearly 12 hours later, plainly visible after dusk through windows of the light-brown home with a large yard.
Investigators combed the property with bomb-sniffing dogs, and Kowalski said more weapons were found.
Sharp's truck was backed up to the home the night before the attack and there was nothing noticeable behind it, said neighbor Randy Mullins.
"Everything seemed good last night," Mullins said. "There was no noise, no nothing. The lights were on."
Matt Payne, who witnessed some of the clash, told the AP he was on his way to work with his wife and 10-year-old son when they heard "this popping sound" while they waited at a red light near the police station. They drove in front of the station and saw the truck engulfed in flames before looking across the street and seeing a man in an open field in an olive-colored flak jacket and carrying what looked like a military-style rifle.
"You know, I don't know if he saw me, but … he was turned my direction when I looked at him. And at that same time, he was turning away to turn his gun on one of the college campus police officers," Payne told CBS' "The Early Show."
Ed Leathers, Collin College's police chief, said the gunman shot several times at a campus officer's patrol car, but the officer was not struck.
Leathers said the officer, a veteran of more than 20 years of police work, was on a routine patrol when he came across the gunman. Several other campus officers were then dispatched to the scene, but none discharged their weapons, he said.