A tenured Yale professor and former Harvard lecturer is under investigation by the United States Attorney's Office for allegedly participating in the exchange of child pornography over the Internet.

Breaking a prolonged silence on the issue, Yale officials announced Tuesday that Antonio C. Lasaga, professor of geology and geophysics, resigned his position as master of Saybrook College and has taken a leave of absence from teaching pending the completion of the investigation.

The school publicly acknowledged the federal inquiry four days after Lasaga's abrupt and then-unexplained resignation. Last Friday he and his wife moved out of the master's residence of Saybrook College, one of 12 Yale student residency halls, which are similar to Harvard's upperclass Houses.

According to several Yale students, agents from the Federal Bureau of Investigation (FBI) raided the master's residence at Saybrook and confiscated several computers Friday.

Prior to the raid, the agents obtained a federal warrant to investigate Lasaga as part of a nationwide crackdown on Internet child pornography rings.

Federal law prohibits trafficking in child pornography over the Internet. No other members of the Yale community are being investigated, according to a statement issued by the university.

The Crimson has learned that Yale officials knew about the federal investigation at least a week before Lasaga's resignation.

Catherine E. McGuinn, a sophomore in Saybrook, said students in the college were informed of the master's departure in a meeting Friday evening.

"[The administration] said Lasaga was leaving for personal reasons and we weren't allowed to ask why," she said.

McGuinn's roommate, Kyle R. Labush, confirmed that college officials told students "not to pry."

"They didn't want questions to be asked," she said.

News of the circumstances surrounding Lasaga's resignation came as a surprise to both Saybrook residents

and students who had contact with him in theclassroom.

"No one saw this coming," said Jessica M.Lichtenstein, a sophomore in "Physical andEnvironmental Geology," an introductory coursetaught in part by Lasaga.

"Professor Lasaga is extremely energetic--youcan tell he's very bright, very student-oriented,"she said. "If you ever needed help you couldapproach him and he would answer questionspersonally."

"Most people are just extremely sad, not evenshocked at the scandal, but shocked at the extentof it," Lichtenstein added.