BOSTON—As shock and horror at the nation’s worst terrorist attack turned to anger and resolve yesterday, the FBI launched the most massive investigation in its history—an investigation that quickly centered on Boston and the city’s ties to suspected ringleader Osama bin Laden.

FBI agents combed Logan airport—the origin of two of the hijacked flights—for evidence early yesterday morning and raided two Boston area hotels yesterday afternoon in a massive operation that shut down much of the downtown area, all in an apparent effort to retrace the last steps of Tuesday’s hijackers.

“We will not stop...We will leave no stone unturned until we have determined who was responsible for these attacks on our freedom,” FBI Director Robert Mueller said yesterday at a Washington press conference.

The FBI convened a special nationwide task force, composed of 4,000 special agents and 3,000 support personnel—including more than 400 lab technicians and forensics experts at the scene of the attack in New York.

The massive investigation stretched from the Canadian border, where officials suspect some of the hijackers entered the country, to Florida, where some of the participants are believed to have learned how to fly commercial jetliners before the attacks. Sealed warrants went out in several other states, officials said. In addition, German police searched at least one location at the request of the FBI.

The FBI has determined the identities of more than a dozen hijackers, several of whom had pilot’s licenses—two of which were registered in Florida.

Authorities detained at least a half dozen people in Massachusetts and Florida on unrelated local warrants and immigration charges and were questioning them about their possible ties to the hijackers. However, no one has yet been charged.

Terrorists And The Hub