September 14 8:57 PM ET

The FBI on Friday named 19 hijackers, including seven pilots, who commandeered the four airliners used in Tuesday's terror attacks, sought to question more than 100 people and made the first arrest in the investigation.

Justice Department officials said investigators arrested a witness with ``material'' information.

Such arrest warrants are issued when the person has information highly relevant to a criminal probe and when there is a flight risk. The arrest warrant was sealed and the officials gave no further details.

The FBI sent to airlines and law enforcement organizations the list of people investigators want to talk to because they may have helpful information about the hijackings, U.S. Attorney General John Ashcroft said.

At the same news conference, FBI Director Robert Mueller said the investigation so far has generated more than 36,000 leads and that agents have conducted hundreds of interviews around the country. Mueller, head of the top U.S. law enforcement agency, said more than 30 search warrants have been served in various locations, hundreds of subpoenas have been issued and agents have seized computers and ``documentary information.''

Mueller declined to say if any of the 19 hijackers have been connected to organizations controlled by Saudi-born militant Osama bin Laden, who has been described by U.S. officials as a chief suspect.

Mueller, a former federal prosecutor who finished his second week on the job, said the FBI had given the investigation the name ''Pentbomb,'' which he even spelled.

But FBI officials later clarified it was ``PENTTBOM.'' They said the ``PEN'' refers to the Pentagon, where one of the hijacked airlines crashed, and the ``TT'' refers to the twin towers of the World Trade Center in New York, where two other hijacked planes crashed into. The fourth hijacked plane crashed in the Pennsylvania countryside.

The officials said the ``BOM'' refers to bomb. When the planes loaded with fuel crashed into the buildings, it was like a huge bomb going off.

The list of names provided no information about the hijackers' national origins, but two of them were in the United States on visas, and the United Arab Emirates was the last known address for one of them.

The hijackers on the flight which gouged a hole in the Pentagon were Khalid Al-Midhar, who was in the United States on a visa, Majed Moqed, Nawaq Alhamzi, Salem Alhamzi and pilot Hani Hanjour, who may have lived in Phoenix and San Diego. No information was available about Moqed, but the Alhamzis were described as possibly residents in Fort Lee, New Jersey.

On one flight that crashed into the World Trade Center, the hijackers were in their 20s or early 30s, and all but one of the five were believed to be pilots, the FBI said.

They were Waleed M. Alshehri, Wail Alshehri, Mohamed Atta, who were believed to have residences in Florida and Hamburg, Germany, Abdulaziz Alomari, and Satam Al Suqami, whose last known address was in the United Arab Emirates.

The hijackers aboard United Airlines Flight 175, which also slammed into the World Trade Center, were pilot Marwan Al Shehhi, who lived in Hollywood, Florida and was in the United States on a visa. The others were Fayez Ahmed, Mohald Alshehri, Hamza Alghamdi and Ahmed Alghamdi, all of whom had addresses in Delray Beach, Florida.

The hijackers aboard the plane which crashed in Pennsylvania were identified as Ahmed Alhaznawi, Ahmed Alnami, Saeed Alghamdi, all possible residents of Delray Beach, and pilot Ziad Jarrahi.

Justice Department spokeswoman Mindy Tucker said the list of more than 100 people that the FBI wants to question went out on Friday, and the names would not be released. She said names would be constantly added and taken off, and she declined to say how individuals had been identified for questioning.

Ashcroft said anyone with information about the hijackers -- even though they are presumed to be dead -- should immediately contact one of the FBI's field offices or call the FBI's toll-free hotline at 1-866-483-5137.

He said the list was sent to 18,000 local police departments, other federal law enforcement agencies, the airlines and the Federal Aviation Administration.