Washington A second arrest warrant for a material witness in the hijackings investigation was issued by federal prosecutors in New York, the Justice Department said Saturday.
The person had not yet been arrested at the time the warrant was issued.
Investigators expected to issue additional warrants as the investigation into Tuesday's attacks shifts into higher gear.
"We are at a point where there will be additional and more frequent warrants," said Justice Department spokeswoman Mindy Tucker.
Meanwhile, 25 people arrested for immigration violations since Tuesday's hijackings have been questioned by the FBI in the investigation, the Justice Department said.
None 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. All are in the Immigration and Naturalization Service's custody.
Tucker said that the FBI may not be finished questioning the 25 detainees. None have been released.
She declined to say whether any of the 25 are suspected of being accomplices to the plot or whether they have significant information about the plot. "It's not clear in all cases how important their information is," Tucker said.
Among them are two men detained at an Amtrak station in Fort Worth, Tex. They were interviewed by FBI agents, taken into custody and flown to New York.
The two boarded a flight Tuesday morning in Newark, N.J., 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.
Some of the 25 were detained because they were discovered to have immigration problems when FBI agents questioned them about the attacks. Others were arrested as part of unrelated investigations and came to the attention of authorities investigating the hijackings.
The immigration problems could range from overstayed or expired visas to being employed without a work visa. The detainees can be held for an indefinite amount of time, and there is no deadline for charging or releasing them.
The INS can detain those arrested for immigration problems for whatever time is deemed "reasonable" to deal with their case, department officials said. Prosecutors sometimes hold foreign nationals on immigration violations as a way to buy time to investigate other charges.
Also Saturday, Atty. Gen. John Ashcroft said the investigation into the attacks was moving forward.
"We are making the kinds of contacts and developing the information that allows us to describe this as proceeding with reasonable success," said Ashcroft, who met with President Bush and administration officials at Camp David.