Nine of the hijackers who commandeered jetliners on Sept. 11 were selected for special security screenings that morning, including two who were singled out because of irregularities in their identification documents, U.S. officials said this week.
Six were chosen for extra scrutiny by a computerized screening system, prompting a sweep of their checked baggage for explosives or unauthorized weapons, authorities said. The ninth was listed on ticket documents as traveling with one of the hijackers with questionable identification.
Law enforcement and aviation officials declined to provide further details about the security screenings, including which of the hijackers were chosen and what flights they were on.
Authorities also said they could not say if any of the nine were interrogated in any way before being allowed to board their flights, or if screeners noticed the box-cutting knives used in the attacks. Such knives were allowed on airplanes before Sept. 11.
But the disclosure that some members of the suicide crews had triggered security measures differs sharply from previous portrayals of the hijackers as meticulous planners who craftily avoided all detection.
It also raises further questions about the adequacy of aviation security measures before the attacks, which have come under increasing scrutiny from some lawmakers and relatives of Sept. 11 victims.
"We are looking into all these accusations of breaches, as well as specific incidents that led up to Sept. 11," said Rep. John L. Mica (R-Fla.), chairman of the House aviation subcommittee. "These are the kinds of questions we are trying to get answered."
One group, Families of September 11, has called for a congressional investigation of possible security lapses that day, including a disputed report that one of the terrorists fired a gun on one of the jetliners. Officials from the Federal Aviation Administration and the FBI say the early report of a gun was a mistake.
"We have a very low confidence level in the Department of Transportation, given what's been going on," said the group's treasurer, Stephen Push, whose wife, Lisa J. Raines, was killed on American Airlines Flight 77. "We want an outside party to investigate this."
The group's concerns stem from an internal FAA memorandum written on Sept. 11 that refers to a shooting on American Airlines Flight 11, which departed from Boston and was one of two jetliners that crashed into the World Trade Center.
The "Executive Summary," citing a report to the FAA by an American Airlines corporate security officer, says a flight attendant on board Flight 11 "informed that a passenger located in seat 10B shot and killed a passenger in seat 9B at 9:20 a.m.," according to copies obtained by The Washington Post and other news organizations.
The document went on to say that "one bullet was reported to have been fired" by hijacker Satam M.A. Al Suqami, and that the victim was passenger Daniel C. Lewin.
FAA and FBI officials, responding to questions about the memo in recent weeks, have repeatedly said the gun reference was a mistake that was corrected in later versions of the same document. American Airlines spokesman John Hotard also said no such report was made to the FAA by an American official.
Instead, officials said, the evidence indicates that Lewin, an Internet company executive and former Israeli special forces officer, was probably stabbed to death along with the two pilots on Flight 11.
"There was a miscommunication," said FAA spokeswoman Laura Brown. "Whether they said weapon instead of knife, or misinterpreted something, we don't know. . . . By the end of the day, they knew that there had not been a gun on the aircraft."
Authorities point out that many other details in the memo have since been proved wrong. Flight 11, for example, crashed into the World Trade Center at 8:45 a.m., not 9:25 a.m., as stated in the memo.
Officials said cell phone calls made from Flight 11, including a recorded call made by a flight attendant, made no mentions of a gun, and FBI investigators have discovered no other reports of guns tied to any of the 19 hijackers.
But Push and other relatives of victims said Congress or another third party should be called in to put the questions to rest.
"At the very least, there has not been a thorough investigation of this memo, because no one seems to have solid information on how this got in the file," Push said. "Even if it was an honest mistake, it casts great doubt on the competence of the people responsible."
Staff writer Don Phillips contributed to this report.