ST. LOUIS -- Security officials evacuated the East Terminal and D concourse at Lambert Airport on Friday after a screener identified a small knife in a piece of luggage but was unable to stop the passenger before the person had left the screening area.

"There was a time delay of about a minute or two, and by that time, the person was gone," said Bill Switzer, the federal security director at Lambert.

Switzer said departures from the East Terminal and D concourse were shut down when the item was discovered about noon, and there was no chance the person was able to board a departing plane. After the two areas were evacuated, airport police searched all planes at the gates in question, finding nothing, Switzer said.

The searches took about 90 minutes, after which passengers were allowed back into the evacuated areas after they had been rescreened. That process was still under way around 3:45 p.m., and lines of passengers waiting to be rescreened stretched out the door of the East Terminal.

Officials said 24 American Airlines and 21 Southwest Airlines flights were affected, and they did not know when the first of those flights would depart. All flights would wait for all passengers before taking off, authorities said.

Switzer said the suspicious item, a three-inch-long Leatherman knife, was next to a spiral-bound notebook in a hanging-style bag. This placement, he said, made the knife appear to be a larger weapon.

The screener, after noticing the item, called over a supervisor to discuss it. During that analysis, which took a few minutes, the traveler picked up the bag and left the screening area.

Switzer said security officials have no leads on the identity of the passenger carrying the knife. He said they do not know if it was a man or a woman. The passenger may not have even been aware knives are now prohibited on planes, Switzer said.

If the passenger goes through again, "he'll definitely be caught," Switzer said.

Switzer said all procedures were strictly adhered to but admitted the time lapse in evaluation that allowed the passenger to leave with the bag could have been shortened.

"Fifteen seconds would have made all the difference in the world," Switzer said.

Officials said the passenger was not immediately detained as screeners evaluated the X-ray because they did not want to tie up lines. Switzer said screeners know when in doubt, a passenger should be stopped.