From the cameras that detect visitors even before they enter the building to the bomb-proof glass in the lobby to the "redundant structural system" that prevents collapse, Seattle's new federal courthouse was designed with threats in mind.

The building opened last summer and was hailed as a huge improvement over the old federal courthouse, where judges, defendants and jurors walked many of the same hallways. The trial of terrorist Ahmed Ressam was moved in 2001 to a newer federal courthouse in Los Angeles, in part because of security concerns with the old Seattle courthouse.

Yesterday's incident, in which a man armed with an inactive hand grenade was fatally shot, was the first real test of the new building's security, and according to an initial review, the system worked, said U.S. Marshal Eric Robertson, whose agency is in charge of courthouse security.

"There is nothing glaring that cries for immediate change," he said yesterday.

For one of the first federal courthouses conceived after the 1995 bombing of the Alfred P. Murrah Federal Building in Oklahoma City, building designers had a difficult task: to provide tight security while still giving the feel of open access.

"It isn't easy to make a building feel welcoming and at the same time have security," Court Administrator Bruce Rifkin said last summer.

The planners handled it not with a single impenetrable barrier, but with layer upon layer of security. This helps explain why yesterday's intruder made it as far as he did, but also why he was stopped.

Like all visitors, the man could get 15 feet or so into the soaring lobby without going through security screening.

In order to get to the courtrooms, the clerk's office or anywhere else, however, visitors must go through a metal detector, which takes up the right side of the lobby. The court security officers who run the metal detectors are armed.

The rest of the large entranceway features what court workers refer to as a moat — a wide, shallow reflecting pool that essentially blocks access to the main part of the building and directs visitors toward the metal detectors.

The capabilities of the reflecting pool were tested yesterday. According to Robertson, instead of going through security screening, the suspect stayed at the far end of the pond, stepped up onto its narrow edge and inched along toward the elevators.

Court security officers spotted the man, who had been in the building numerous times, and told him to stop. Cameras, meanwhile, detected the grenade in his hand. The guards knew that the entranceway serves as sort of a "front porch" to the building, so that intruders who make it into the lobby are not under the building's main core.

Security officers "cordoned him off so he could not enter the secure portion of the building," Robertson said.

He was shot just beyond the moat.

In addition to the reflecting pond and security screening, the building has floor-to-ceiling windows with special glass that protects against bomb blasts. The building is set back from the street, with a large plaza on one side, a blocklong staircase on another, and concrete barriers. These features would help prevent a truck bomb.

In 2001, after someone sent anthrax in letters through the mail to media and government offices in Washington, D.C., Florida and elsewhere, building designers added a special ventilation system for the mailroom.

Maureen O'Hagan: 206-464-2562 or mohagan@seattletimes.com