Mayhew initially called KUTV, just across the street from the station, about 9 p.m. He told a staffer that he was on the train station's platform with a bomb that he intended to explode. KUTV immediately called 911.
Mayhew told the first officer who arrived that he needed help and did not want to hurt anyone. The officer saw a cord running out of his backpack to a black device with a button in his right hand. The officer convinced Mayhew to remove his thumb from the button so that he would not accidentally detonate the bomb.
SWAT set up a perimeter around Mayhew as police negotiated with him and cleared the area. Mayhew said his bomb included 10 to 15 shotgun shells attached by wires to a battery and the trigger in his hand, and that it had a blast radius of 40 yards.
But when a bomb squad technician arrived and heard about Mayhew's device, he warned the officers that it could have a blast radius seven times greater than what Mayhew had told them. Police expanded their perimeter and ordered bystanders on the sidewalks farther back.
Mayhew knew what he was talking about when it came to explosives, which gave his threats a legitimacy, said District Attorney Sim Gill.
Mayhew sat down on a decorative rock, but was visibly upset and agitated. Sweeny noticed that he was tapping his foot, his back was shaking and that he wiped his eyes as though he were crying.
Sweeny said that Mayhew then appeared to "prepare himself for something" or was "squaring himself away" as he gathered his belongings and took a few steps north and closer to the containment line, according to the letter. Another officer shouted at Mayhew not to move, loud enough that the words echoed throughout Main Street.
Mayhew turned and advanced toward another officer, yelling that they would have to shoot him, and his left arm went toward the backpack.
"Sweeny said he feared for his safety, along with the safety of the other officers and the public within the blast radius," according to a letter from the district attorney's office.
About 11 p.m., Sweeny fired one round from his M-4 SWAT issued rifle, striking Mayhew in the chest. He was declared dead at the hospital.
"It's not the result that we wanted," said Police Chief Chris Burbank. But he was proud of his officers' patience, and that they gave Mayhew every opportunity to surrender.
The district attorney's investigation found that Sweeny was justified in shooting Mayhew. Gill noted that Sweeny acted only fractionally quicker than other officers who were about to pull the trigger as well.
Improvised explosive devices are "very scary" to deal with, and officers have to treat the threat like it could do some significant damage, Burbank said.
Police used a robot to neutralize the device. It was impossible for investigators to figure out the exact destructive potential of the device from the remains of the disrupted bomb, but from the glance at the materials that made up the device from a robot, it was determined that it couldconstitute an explosive device. The bomb technician also figured its radius could reach 850 feet based on what Mayhew told police.
Police later found designs and materials to build the bomb in Mayhew's bedroom.
Mayhew had a long criminal history. In 1995, he was charged in 3rd District Court with five felonies, including aggravated assault and aggravated kidnapping. In 1996, Mayhew and another man were charged with a felony hate crime. Utah court records also show a number of assaults and drug-related offenses dating back to 1992.