(CNN) -- In the photo, the middle-aged man is seated and leaning back, the pose and a couple bags next to him suggesting he's catching his after breath after a rigorous round of shopping.
But investigators said Friday they consider the man as potentially involved in something sinister -- the planting of a pipe bomb and two propane tanks at Southwest Plaza Mall in Littleton, Colorado.
The FBI Denver Joint Terrorism Task Force released three more photos of the gray-haired man, shown leaving the mall on a bus Tuesday night, several hours before the incident.
They are the clearest views of the man seen wearing the same clothing on Wednesday, when the mall was evacuated after a related fire.
Authorities told reporters at a news conference Thursday that the man they are seeking is a "person of interest."
Friday, the description of him was bumped up to "possible suspect."
Police asked for public help as they investigate the possible attempt to bomb the shopping center on the 12th anniversary of the shooting at nearby Columbine High School that left 12 students and a teacher dead at the hands of two other students, who then killed themselves.
No evidence exists so far of a link to the Columbine shootings, Jefferson County Sheriff Ted Mink said, but he acknowledged the possibility was on the minds of law enforcement officials.
"There's not a definite link that we have right now to anything at Columbine other than the date," Mink said, adding that the April 20 anniversary of the shootings "is fresh on everyone's mind."
A security camera shows the man sought by authorities in the mall just minutes before a security guard extinguished the fire.
Investigators say that fire may have been part of an attempt to detonate explosives.
Mall store employee Marshall Wood told CNN Friday that he called security after seeing the fire in a panel in the hallway behind the store.
Wood said he noticed one or two small green propane canisters near the blaze.
"Its pretty scary that it was right next to my store."
Wood said he has seen surveillance photos of the man.
"I wouldn't have thought twice if I saw him in the mall," Wood said. "He looked like a normal shopper or mall walker."
Law enforcement officials Thursday released surveillance camera images of the man carrying a white plastic bag at the mall around noon Wednesday. He was in a part of the mall that the public does not usually access.
A subsequent search turned up explosives, said Jacki Kelley of the Jefferson County Sheriff's office.
"The propane tanks and the pipe bomb were literally together," she told reporters Wednesday night at a news conference.
The mall was quickly evacuated and no one was hurt, authorities said.
Mink said that the mall had been thoroughly searched and was allowed to reopen on Thursday. None of the authorities provided further information on the explosives found at the scene, saying they needed to interview more people and didn't want details reported in the media to influence any responses they might get.
The situation could have been much worse, said Dave Joly, a spokesman for the FBI.
"Depending (on) if it went off and actively combusted as what it was set to do, it could have been more serious than it was," he said at an earlier news conference, adding that it appeared that the pipe bomb was supposed to be a trigger to detonate the propane tanks.
The person authorities want to talk to is described as a white male with gray hair and a silver mustache, the FBI said. He wore a dark cap with a light-colored logo on the front, a gray and white horizontally striped shirt, a dark jacket, jeans and dark-colored shoes.
CNN's Jeanne Meserve contributed to this report.