NEW YORK—Jury selection began Monday in the trial of two men charged with conspiring to rape, torture and murder women and children as a judge said he was inclined to let jurors hear testimony about an "extremely disturbing" video found in a former Manhattan school librarian's apartment and a conversation with an undercover investigator in which he expresses sexual interest in infants.

U.S. District Judge Paul G. Gardephe said he had not yet made a final decision, but believed both pieces of evidence had relevance to the charges against 61-year-old Robert Christopher Asch, a former librarian at Stuyvesant High School in lower Manhattan.

Also on trial is Michael Vanhise, 23, of Trenton, N.J. in a case that stems from the prosecution of Gilberto Valle, a former New York City Police officer convicted last year of plotting to kill and eat women. Valle is awaiting sentencing.

Verbal questioning of potential jurors was set to begin Tuesday after about 100 prospective New York jurors filled out questionnaires Monday aimed at learning if they can be fair and impartial despite the ghastly nature of the evidence.

One prospective juror shook her head slowly as Gardephe warned that the evidence includes discussions of kidnapping, raping, torturing and murdering women and children. She put her head in her hands as the judge said defense lawyers were likely to assert that the conversations were sexual fantasy and imaginary role-play.

Gardephe said he viewed a roughly half-hour "pain video" before deciding it was likely relevant to the charges against Asch.

"It's a graphic tape. It's not a staged event or phony event. It appears to be real," the judge said. "The video is extremely disturbing."

He said he was likely to let an agent testify about the sexual instruments used on women in the sadistic video because prosecutors say the instruments are similar to those that Asch brought to a meeting with an undercover agent. But Gardephe said he was likely to require the agent to testify outside the presence of the jury first so he can clearly define the scope of the testimony.

"The fact it's disturbing doesn't mean it doesn't shed light on Mr. Asch's state of mind at the time or his intent with what he would do with the instruments," the judge said.

He said the conversation with the investigator in which Asch expresses sexual interest in infants was relevant to a conspiracy charge that accuses Vanhise and Asch of plotting to rape and murder women and children.

He said a portion of the conversation by Asch in which he described it as fantasy could be used by the defense to show he never intended harm.

Defense attorney Brian Waller said the statements "could be exculpatory but also very inflammatory."

Gardephe replied: "The statements are extremely disturbing. I don't disagree with you on that."

Assistant U.S. Attorney Hadassa Waxman said the conversation was "absolutely relevant" to the charges and "critical evidence."