In Montoursville, Pa., residents attend a memorial service for the students killed in the crash. (AP Photo)

The investigation of TWA Flight 800's violent destruction almost immediately took a different tack from probes of most other airliner crashes, as the possibility of a terrorist attack led federal law enforcement officials to assume an unusually early and prominent role in the inquiry.

Usually, the National Transportation Safety Board launches crash inquiries on its own, following a practiced investigative method and hands over the investigative lead only if its staff finds evidence of tampering, air safety experts said.

But less than 24 hours after the Paris-bound airliner crashed, a task force on terrorism run jointly by the Federal Bureau of Investigation and the New York City Police Department announced it would "assume leadership of the investigation into the circumstances surrounding the possible explosion." The faxed statement was sent to news media shortly after 3 p.m. Thursday even as the safety board's lead investigator, Robert Francis, was telling reporters in East Moriches that there was no evidence of criminal involvement and that the NTSB was in charge.

Air-safety experts say the NTSB usually has sole authority in crash inquiries. "Until there's evidence of foul play, NTSB is in charge of the investigation," said Charles O. Miller, a former director of the NTSB aviation safety bureau who has worked as an international safety consultant for the past two decades.

The bureaucratic boundary remained confusing thoughout the day. At a news conference Thursday afternoon, Gov. George Pataki declared that the FBI was treating the accident area as a potential crime scene -- prompting Francis to return before reporters and re-emphasize that his board was in charge of the investigation.

Early in the day, observers at the crash scene said evidence was being deposited within a few feet of a Red Cross lunch truck, and people involved in the rescue were eating bagels and cream cheese where evidence was being tagged. The FBI roped the area off about 3:30 p.m. and declared it a hazardous-waste area, requiring anyone who entered to be wearing protective gear.

FBI officials said the two agencies would continue to cooperate on parallel investigations. While safety board officials are determining the physical causes of the crash, the FBI's investigation will focus on catching the people responsible for the destruction of the plane -- if it is determined that the explosion was planned. Unlike the NTSB, law enforcement officials view the remains of the plane as evidence that needs to be preserved for a criminal trial, not just clues to solve the puzzling end of TWA Flight 800.

Airline safety experts said the NTSB would pursue its investigation into the crash by creating a series of teams, made up of its own staff as well as experts from all fields in the airline business: investigators from the pilots union, the airline and the manufacturers of the plane and the engine.

One team typically looks at what happened to the plane's body. A bomb explosion, experts said, leaves an imprint and chemical residue that are easy to identify.

Another team is in charge of the engines, while a third team examines the flight and tries to recreate the path of the airplane before it crashed. Another team focuses on "human factors," any errors that may have been made by pilots or controllers; still another team reviews the "black box" flight data and cockpit voice recorders. Others interview witnesses, flight controllers and survivors, when there are any.

The Flight 800 investigators are using a hangar at the former Navy airfield at Calverton to put together the wreckage of the plane piece-by-piece to see where an explosion or malfunction might have occurred.

The entire investigation can last months and will end with a public hearing, typically about nine months later and a written report intended to identify a primary cause and contributing factors.

Experts said the investigators usually can conclude within a few weeks what caused a crash, but members of the team are barred from speaking publicly about their investigation until the report is concluded.

Robin Topping and Michael Slackman contributed to this story.