A man who helped two Sept. 11 hijackers fraudulently obtain Virginia identification cards also misled FBI agents into believing other attacks were imminent, a prosecutor said Thursday.

Luis Martinez-Flores, 28, pleaded guilty to document fraud for signing forms falsely certifying that Hani Hanjour and Khalid Almihdhar, hijackers on the flight that crashed into the Pentagon, were state residents. The hijackers paid him $100.

At Thursday's plea hearing, a prosecutor said Martinez-Flores exaggerated his connections to the hijackers and told the FBI that Hanjour had discussed attacks on Federal Reserve banks, stadiums and other large buildings on the East Coast.

After a time-consuming investigation, authorities discovered that Martinez-Flores made up the story, prosecutor John Morton said. Morton said Martinez-Flores, an illegal immigrant from El Salvador, apparently lied "to make himself appear more important to the government."

Prosecutors have not said whether Martinez-Flores knew about the hijacking plot before Sept. 11.

Martinez-Flores said through an interpreter that his lies were "a grave mistake on my part." Asked why he lied, he said: "I was terrified and I didn't think of where this was going to end."

U.S. District Judge T.S. Ellis III also criticized Virginia for the loophole that allowed applicants to obtain ID cards without proof of residency or identity. The motor vehicle department changed its rules Sept. 21.

Martinez-Flores is one of four people who have pleaded guilty to document fraud in connection with the Sept. 11 investigation. All await sentencing.