NEW YORK (AP) — In a room in the 9/11 museum, there are a police captain's poignant notes and a flashlight that illuminated the way to safety. Nearby, a letter from a trapped man tells his family, "I love you very much.... Do wonderful things in your life."

The artifacts aren't from Sept 11, 2001. They are reminders of a terror attack that foreshadowed it: the deadly World Trade Center bombing, 25 years ago Monday.

That shadow fell personally on Lolita Jackson. As a young finance worker, she picked her way down 72 flights of blacked-out stairs on Feb. 26, 1993, and fled the trade center's south tower again in 2001.

The bombing "tends to be forgotten because 9/11 was such a cataclysmic event," she says, but the blast has its own place in the lives and memories of an estimated 50,000 people who were in the twin towers that snowy afternoon.

The explosion killed six people, injured over 1,000, manifested the growing terror threat from Islamic extremism and led to safety improvements credited with helping some people survive Sept. 11.

It "was, in many respects, a precursor to 9/11," says museum President Alice Greenwald.

A bomb exploded in a rented van in a basement parking garage shortly after noon, causing a crater several stories deep and a boom felt many floors above.

The blast killed visitor John DiGiovanni and five people who worked at the trade center — Robert Kirkpatrick, Stephen Knapp, William Macko, Wilfredo Mercado and Monica Rodriguez Smith. Smith was pregnant.

Power was knocked out and pipes were severed, flooding backup generators. Elevators got stuck. A group of kindergartners was stranded for hours on an observation deck. Other people were trapped in the debris-filled garage. Police helicopters plucked nearly two dozen people, some disabled, from rooftops.

Some office workers broke out windows to try to clear smoke while awaiting help. Others made their way down, emerging coated in soot.

Jackson didn't feel fearful at first. What was terrifying was the 2 [1/2]-hour trek down the pitch-dark, crowded, smoky stairs, wondering what she would see at the bottom.

"You didn't know what was going to happen," recalls Jackson, who now works in city government.

Alone in a stalled elevator with smoke wafting in and no idea why, trade center worker Carl Selinger began to think he might not get out alive. So Selinger wrote a letter to his wife and children and waited. He was rescued after 5 ½ hours.

"I dealt with what I had to deal with," Selinger said at a recent discussion at the Sept. 11 museum.

Within days, a fragment of the rented van began leading investigators to Muslim extremists who sought to punish the United States for its Middle East policies, especially its aid to Israel, according to prosecutors.

As they pursued that case and learned about another plot to bomb New York City landmarks, then-Manhattan U.S. Attorney Mary Jo White "saw red lights blinking everywhere about how serious I thought this threat was from international terrorists," she told an audience Thursday at the museum.

Indeed, a letter found on an accused bombing conspirator's laptop made it chillingly clear the threat wasn't over.

"Unfortunately, our calculations were not very accurate this time. However, we promise you that next time it will be very precise and the World Trade Center will continue to be one of our targets," it said.

Six bombing suspects were convicted and sentenced, including accused mastermind Ramzi Yousef — a nephew of Khalid Sheik Mohammed, who would later become the self-professed architect of 9/11. A seventh bombing suspect, Abdul Rahman Yasin, remains at large and is on the FBI's list of most wanted terrorists.

After the bombing, the government-run trade center banned underground parking, installed battery-operated lights in stairwells and added security cameras, among other safety upgrades.

A memorial fountain was destroyed on Sept. 11. But bombing victims' names are now inscribed on one of the waterfall pools that bear the names of the nearly 3,000 killed on 9/11. A room in the Sept. 11 museum is devoted to the bombing, and a special temporary installation marks the 25th anniversary.

After poring through the installation one day recently, 15-year-old Raven Rucinski, of Michigan, was surprised she'd never heard much about the bombing. Catlin Roberts, 39, from Swansea, Wales, reflected on the legacy of an event she had only dimly recalled.

"I don't think, when this happened, people understood what the people who did it represented," she said.