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. Last Updated: 07/27/2016

Terror Probe Picks Up Steam

WASHINGTON -- With one man in custody in New York, authorities investigating the terrorist attacks issued a second arrest warrant for a material witness and detained 25 people for possible immigration violations.

"We are beginning to understand the ways in which this terrible crime was committed," Attorney General John Ashcroft said Saturday.

The FBI has received over 36,000 leads and has issued hundreds of subpoenas. It released the identities Friday of the 19 hijackers.

Authorities said they were still investigating whether more terrorists might be at large and were searching for 100 people for questioning.

"We are at a point where there will be additional and more frequent warrants," said Justice Department spokeswoman Mindy Tucker.

Authorities made their first arrest in the case Friday. A man described as a material witness in the attacks was taken into custody in New York. Officials speaking on condition of anonymity said the man arrested was the same person detained Thursday at John F. Kennedy International Airport with a fake pilot's license.

None of the 25 held on immigration violations has been formally charged, either on immigration counts or with crimes related to the four hijackings, Tucker said.

Some but not all of the detainees who have been interviewed are cooperating with the FBI.

Tucker declined to say whether any of the 25 are suspected of being accomplices to the terrorist attacks or whether they have significant information about the plot.

Among the 25 are two men detained at an Amtrak train station in Fort Worth, Texas. They were interviewed by FBI agents, taken into custody and flown to New York.

The two -- Mohammed Jaweed Azmath and Ayub Ali Khan -- boarded a flight Tuesday morning in Newark, New Jersey, as the four hijackings were under way, said a law enforcement source, speaking on condition of anonymity. The plane was grounded in St. Louis as the FAA halted all air traffic; the men then boarded an Amtrak train bound for Texas.

They were taken off during a routine drug search Wednesday night. Although no drugs were found, the men had box-cutting knives, authorities said, and also carried about $5,000 in cash, according to a federal official who spoke on condition of anonymity.

The hijackers had used knives and box cutters to take control of the planes.

Meanwhile, searchers on Friday recovered the "black box" voice recorder from United Airlines Flight 93, which crashed near Pittsburgh. The jet's flight data recorder was recovered earlier. Two recorders also have been recovered from the Pentagon crash scene.

The FBI's list of 19 suspects who commandeered and brought down the planes showed that many lived in Florida and several had gone to pilot training school in Venice, Florida.

Some of the 19 have been linked to Osama bin Laden or his organizations, according to current and former U.S. officials.

The officials said four of the dead hijackers had been linked to bin Laden's Al-Qaida network: Waleed Alshehri, Ahmed Alghamdi, Hamza Alghamdi, and Saeed Alghamdi. Among the 19 was Mohamed Atta, 33, of Hollywood and Coral Springs, Florida, identified by German authorities as being tied to an Islamic fundamentalist group that planned attacks on American targets. The Justice Department said Atta was aboard American Airlines Flight 11 that took off from Boston's Logan Airport and crashed into the north tower of the World Trade Center.

All the hijackers had Middle Eastern names.

Law enforcement officials said two of the alleged hijackers had been added to a terrorist watch list a few weeks before Tuesday's attacks. One of the men was Khalid Al-Midhar, an alleged hijacker aboard an American Airlines flight that smashed into the Pentagon.

Newsweek magazine said Al-Midhar had been captured on a surveillance videotape in Malaysia meeting with one of the suspects in the Oct. 12, 2000, terrorist bombing of the USS Cole in Yemen.

Newsweek identified the other man as Salem Alhamzi, another alleged hijacker of the American flight.