SEATTLE -- A Seattle schoolteacher accused of possessing child pornography pleaded not guilty before a judge on Tuesday.

Timothy Sheehan, 50, is charged with one count of possession of depiction of minors engaged in sexually explicit conduct. He is on leave from his job at Whitman Middle School in Seattle.

Sheehan's attorney called the allegations "baseless."

"He's somebody who's worked in the school district for 24 years now. He's worked at the same school for 18 years. There's not been a single allegation against him at any point in time of any kind of wrongdoing," said Jeff Cohen.

The investigation began after a woman who said she dated Sheehan told police he showed her child pornography on his computer.

The woman, who said she broke up with him in early May, said Sheehan "talked ... about killing young boys" and fantasized "about having sex with underage boys," according to a search warrant obtained by KIRO 7 Eyewitness News.

According to the documents, Sheehan told his former girlfriend that he was a "pedophile" and a "rapist."

A laptop computer, according to documents, was one of many things seized from the Sheehan's North Seattle home, along with external hard drives, videotapes, photos and yearbooks.

Cohen said he is waiting to see the prosecutor's evidence.

"This is just an allegation by a woman who used to be his lover and that there aren't any facts to substantiate," Cohen said.

The charge is a class C felony, which carries a standard sentence range of up to one year in jail.