NEW HAVEN, Conn. (May 22) - FBI agents investigating a bombing at Yale University's law school dusted for fingerprints Thursday and showed students a sketch of a man seen leaving the empty classroom just before the blast.

The explosive - which investigators believe was a pipe bomb - damaged two rooms Wednesday, and about 300 rare law books in a room below were soaked with water from the sprinkler system. No one was injured.

Acting Police Chief Francisco Ortiz said the bomber was ''trying to send a message.''

Law student Carsten Jungmann said he helped the FBI draw a sketch of a man he saw leaving the classroom about two minutes before the explosion. The man was clean-shaven and appeared to be in his 20s or 30s, with black hair that hung just below the ears, Jungmann said.

''He appeared to be not suspicious at the time, but he was moving more quickly than people normally appeared to move through the law school,'' he said.

FBI did not immediately return calls for comment on the sketch. And police said they had no suspects.

Investigators said that because the bomb appeared to be small, and went off in an empty classroom, the blast was probably not the work of international terrorists. But they said they have not established whether the bomb went off too soon or late or whether it was intended to be more powerful.

No threats were made before the explosion, and no one claimed responsibility, police said.

A university source with firsthand knowledge of the investigation told The Associated Press that authorities strongly believe the device was a pipe bomb.

Bomb experts went through the classroom on their hands and knees in a search for shrapnel, swabbed for explosives or other evidence and took fingerprints from doorways and furniture. The FBI interviewed students, faculty and staff members who were in the building at the time.

Ortiz said investigators would be looking at whether the date, the room or anything else about the law school held any meaning for the bomber.

Thursday was the birthday of Theodore Kaczynski, the Unabomber. He is serving a life sentence for attacks that killed three people and wounded 23 from 1978 to 1995. One of those bombs maimed Yale professor David J. Gelernter when it exploded in his campus office June 24, 1993.

Mayor John DeStefano said there was no indication the birthday and Wednesday's bombing were linked.

Several students reported seeing a fireball in the corridor outside the classroom, which was used by various professors all semester. A partition between the room and a faculty lounge collapsed, and some of the ceiling also fell down, littering the room with debris, police said.

The damaged books included volumes printed in 16th- and 17th-century Europe, said Roberta Pilette, who oversees preservation for Yale's Beinecke Rare Book and Manuscript Library. A freeze drying machine at the library would be used to dry out the books, she said.

''The books will be useable. I don't think we lost anything at all,'' Pilette said.

Commencement ceremonies still were scheduled for Monday, though a heavy police presence is planned. Police are also discussing whether to use metal detectors and search guests' bags.

The law school building remained closed Thursday, and students were not allowed to retrieve their belongings from rooms and lockers.

The explosion with the nation on elevated alert for terrorist attacks and several hours after President Bush - a Yale alumnus - spoke at the U.S. Coast Guard Academy graduation ceremony in New London, about 50 miles to the east.

One of the president's daughters, Barbara, is an undergraduate at Yale. Secret Service spokesman John Gill said she was ''not in danger at any time and she was not in the vicinity'' of the blast.

AP-NY-05-22-03 1634EDT

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