"We do not know why he did it," said UW Assistant Police Chief Ralph Robinson, adding the man suffered second- and third-degree burns. "That's a big mystery."
The man had been part of the university's support staff, Robinson said. He said he didn't know what department the man worked in, or when or why he left.
Witnesses in Red Square, a large brick plaza at the center of the Seattle campus, reported seeing "this big flame and a ball of fire" around 1 p.m. Thursday, Robinson said.
Student Trevor Preston said he was walking out of a library when he saw the man in the middle of the plaza pouring liquid on himself from a large container.
"Everyone was eyeing him because we couldn't comprehend that he was actually pouring gas on himself," Preston said.
One onlooker ran toward the man in an apparent attempt to stop him, but slipped on the liquid before he could reach him, witnesses said.
Student Dan Kim said the man, who appeared to be alone, "lit a match and all of a sudden everything went up in flames, including himself. He dropped down onto the ground. He was rolling on the ground."
Several people, including student Peter Chung, rushed toward the man and tried to smother the flames with their jackets, shirts and other clothing. A few ran to get fire extinguishers, he said.
"A bunch of us used our water bottles to try to kill the fire," Chung said.
One man took off his jeans and stood in his boxers trying to douse the flames, witnesses said.
Dan Kim said the badly burned man was mumbling incoherently when the flames were finally put out. Kim said he heard the man say "Oh my God" before he was put into an ambulance.
Robinson said no campus demonstrations had been going on at the time and that "it appears this was just a single event."