A U.S. State Department employee in Antigua suspected that John Allen Muhammad had committed a crime by giving her a forged birth certificate in November 2000 bearing the name Thomas Lee in an unsuccessful attempt to obtain a U.S. passport.

The consular agent, Julie Ryder, passed the information on to her superiors. But State Department investigators never obtained a warrant for the arrest of Muhammad, who along with John Lee Malvo has been charged in the sniper attacks in the Washington area and shootings in other parts of the country.

In the two months after Ryder linked Muhammad to the Thomas Lee alias, Muhammad entered the United States at least twice using the Muhammad name. If the State Department had obtained a warrant for his arrest for making false statements to obtain a passport, he would have been detained when he tried to return to the United States and faced a federal charge carrying a sentence of up to 10 years in prison.

Stuart Patt, a State Department consular spokesman, said officials have launched an internal investigation into how the Muhammad matter was handled. He said he could not comment further on the case, citing privacy rules. Ryder declined to comment.

A State Department official, speaking on the condition of anonymity, said that failing to obtain warrants for such offenses "is a common phenomenon." The official said that until the terrorist attacks of Sept. 11, 2001, most federal prosecutors treated such cases as a low priority.

The official said that "in a perfect world," a warrant would have been obtained for Muhammad's arrest. "But until recently," the official said, "we haven't been finding a lot of U.S. attorneys who were willing to prosecute on this."

The official was uncertain whether the State Department's Diplomatic Security Service, which investigates passport fraud, had even sought a warrant from a U.S. attorney's office for Muhammad's arrest.

Bryan Sierra, a spokesman for the Justice Department, said he could not find data to indicate whether the rate of passport fraud prosecutions was lower before Sept. 11, 2001. Since then, he said, U.S. attorneys have aggressively prosecuted many such cases.

"I don't have any data to rebut the State Department in any way," Sierra said.

U.S. Rep. F. James Sensenbrenner Jr. (R-Wis.), chairman of the House Judiciary Committee, said yesterday that he has asked his staff to investigate the matter.

"If true, the State and Justice Departments share responsibility for this failure, regardless if it occurred pre-9/11," Sensenbrenner said in a written statement. "Fraudulent documents expose the American people to a serious terrorist and criminal risk that they would not face if these departments fully enforced our laws."

Authorities in Antigua who have been investigating Muhammad's activities on the Caribbean island in 2000 and 2001 say he made money by providing false documents to people so that they could illegally enter the United States. Muhammad, who fled to Antigua with his three children during a divorce and custody battle with his second wife, used a number of aliases, authorities said.

In a recent report updating their investigation of Muhammad, authorities in Antigua cited a memo that Ryder wrote to police on the island.

"The letter raised very cogent questions about who he was and names he was using," the investigation summary from Antigua said. "That knowledge went into American government files and we don't know if it was ever followed up on."

According to Ryder's memo to an Antiguan police investigator, Muhammad went to the U.S. consular office on Nov. 8, 2000, and presented a Pennsylvania birth certificate identifying him as Thomas Lee. She wrote that the document "looked strange," prompting her to forward a copy to other U.S. officials who confirmed that the document was false. Muhammad did not receive a passport.

It was not until March 2001 that Ryder seems to have matched the Thomas Lee alias with Muhammad. That month, Muhammad turned up at the Antigua airport with a birth certificate and driver's license in someone else's name and tried to check in for a flight to Los Angeles with a ticket paid for in cash. Authorities believe that another man was to board that flight in his place.

Muhammad was taken into custody, and police alerted Ryder. They told her of a number of names the man was using, officials said, including Lee and Muhammad. Muhammad slipped out of police custody, and authorities on Antigua have not been able to explain how.

That prompted Ryder to write the memo to police outlining the facts of the case, starting with Muhammad's attempt to obtain a passport in November 2000. The memo asked police to review what she had written before she forwarded it to the U.S. Embassy in Barbados.

Officials at the State Department said yesterday that they were unsure when Ryder alerted the embassy. The State Department official who spoke on condition of anonymity said that the case eventually was entered into a computer database listing people suspected of using fraudulent documents and that a regional office of the FBI was notified.

That was not enough to prevent Muhammad's entry into the United States. Officials said that without a warrant for his arrest, the Immigration and Naturalization Service could not have detained him because he is a U.S. citizen.

In April 2001, Muhammad flew into Miami International Airport. He was with two Jamaican women and a young girl. Muhammad presented a false birth certificate, and the women and the child also presented false documents, according to law enforcement sources familiar with the case.

One source said that INS officials suspected Muhammad might be involved in smuggling the women and the girl into the country but that they did not develop enough evidence to make a case. The INS questioned Muhammad about whether he was a U.S. citizen. The agency concluded that he was and allowed him to enter the United States. He was not charged with presenting false documentation at the airport.

Muhammad then traveled from the United States to Antigua on May 20, 2001, this time using documents listing his name as Muhammad, said John Fuller, who is heading a commission appointed by the Antiguan government to investigate the sniper suspects' activities on the island.

Muhammad returned to the United States on May 31, 2001, along with Malvo, who was traveling under the name of Muhammad's son from his first marriage, Lindbergh, according to Fuller.

More than a year later, authorities say, Muhammad and Malvo embarked on the cross-country trip that culminated in the series of sniper shootings in the Washington area.