OKLAHOMA CITY (AP) _ The day the nation's television stations broke into morning shows to show a nine-story Midwestern building _ its front sheared off, gray smoke billowing from every crevice _ is just a memory for most.

However, for thousands in Oklahoma City, and those drawn daily to a Colorado courtroom, the worst bombing in U.S. history is being relived.

In Denver, some are nervous about dredging up the details of April 19, 1995. In Oklahoma City, the dust never settled for those who lost sons, daughters, husbands, wives, mothers, fathers, and friends.

``It doesn't feel like two years,'' Maureen Bloomer said. ``I'm still trying to get my life together. Sometimes, it feels like just a month ago.''

Ms. Bloomer's father, Olen Bloomer, was working as a budget assistant for the U.S. Department of Agriculture when the Alfred P. Murrah Building housing his office blew up shortly after 9 a.m. It took 16 days for his body to be pulled from the rubble.

``He was my best friend,'' said Ms. Bloomer, 31, whose mother died five years earlier. ``I don't have a family anymore.''

Cathy McCaskell's sister, Terry Rees, was at her job at the U.S. Department of Housing and Urban Development that morning. Mrs. McCaskell, 39, waited six days before her sister's body was found.

``With the trial coming up, it's kind of bringing it back up,'' Mrs. McCaskell said. ``It's a place I don't want to go to in my mind. It really hurts. Others have gone on with their lives and we haven't _ we're still stuck.''

The usual thing to do is wait for time to fade away the memories of that morning and the loss of loved ones. But the door to that healing process slammed shut with the opening of the trial of Timothy McVeigh, the 28-year-old former Army soldier accused in the blast that took 168 lives.

News accounts of jury selection are a daily event. Coverage and details of the blast will only increase when testimony begins, and could continue unabated for months.

``I don't think people can really begin closure until this trial is over,'' said Charlotte Lankard, assistant director of the Outpatient Counseling Center at Integris Baptist Medical Center in Oklahoma City. ``Two years later, it's real.''

In Denver, some of what is happening seems surreal.

The trial, a missing Air Force warplane carrying four 500-pound bombs, and a mysterious threat against the nation's air defense agency have created an air of cautious concern across much of Colorado.

``It seems a funny coincidence that it all happens at once,'' said Marilyn Winders of Montrose, Colo., who was visiting Denver over the weekend. ``You kind of wonder if it's all tied together.''

At Colorado Springs, security was tightened and tours canceled at the North American Aerospace Defense Command on Wednesday because of an unspecified security threat.

Earlier this week, a man with a .357 handgun was arrested near the Denver courthouse, accused of making threats against the FBI. On the back of his pickup truck were bumper stickers that read ``Sniper Bar and Grill, all you need is one shot'' and ``Keep your hands off my arms.''

Factored into the equation is the two-year anniversary of the Oklahoma City bombing, which is also fourth anniversary of the Branch Davidian compound near Waco, Texas, burning to the ground. The FBI's siege of the compound is why prosecutors claim McVeigh blew up the Murrah building.

``We're at increased awareness,'' said Polly Baca, Colorado's regional administrator of the General Services Administration. ``That (Denver courthouse) building is at the highest security and is above the national standards for top security for federal building with civilian employees.''

David Richendifer of Denver said he has noticed added security in downtown hotels and office buildings where his company makes deliveries.

Although he isn't concerned about the anniversary, ``I wouldn't be surprised if something happened,'' he said.