A mall near the site of the 1999 Columbine High School massacre has resumed operations after officials said someone tried to detonate a bomb inside the shopping center.

Firefighters found a pipe bomb and two propane tanks inside Southwest Plaza Mall in Littleton, Colo., April 20 -- the 12th anniversary of the Columbine school shooting rampage.

The bomb failed to detonate, but the explosive devices were similar to those used in the Columbine tragedy.

"Having it happen on April 20 when you literally can see the high school from here, knowing that this community was so highly impacted by what happened 12 years ago -- this is a sensitive day for all of us," Jefferson County sheriff's spokeswoman Jacki Kelley said. "It's something that can't be ignored and won't be ignored."

Investigators have released three photos of the bombing suspect, two of him entering a mall stairwell carrying a white plastic bag and another of him on an escalator.

The suspect, who is not in custody, set a small fire next to the propane tanks. He is described as a white male with graying hair and a silver mustache.

On April 20, 1999, two teenagers shot and killed 13 students at Columbine High School, which is about two miles from the mall.