RALEIGH, N.C. — A former CIA contract worker charged with beating an Afghan detainee who later died said he assaulted the prisoner during an interrogation, a fellow agency employee testifying in disguise said yesterday.

David Passaro is charged with beating Abdul Wali over two days in June 2003 while questioning the man about rocket attacks on a remote base housing American and Afghan troops.

Mr. Passaro is the first American civilian charged with mistreating a detainee during the wars in Iraq and Afghanistan.

“He told me that he had struck him,” the other CIA contractor testified under the pseudonym Randy Wilson. “I was quite surprised about that.”

Mr. Wilson added: “He said he thought Wali was going after someone, one of the other persons present during one of the interviews.”

Mr. Wilson was one of three CIA employees who testified yesterday in disguise and under assumed names.

U.S. District Judge Terrence Boyle did not say what had been done to alter the witnesses’ appearance, but all three had full hair, thick mustaches, and glasses. The judge ordered a courtroom artist not to draw their faces.

Mr. Passaro, 40, who is charged with assault — not in Wali’s death — could get up to 40 years in prison.

Defense attorneys say the former Special Forces medic never hit Wali and gave the detainee mouth-to-mouth resuscitation on the day he died.

The other two witnesses, a career CIA agent and another contract worker, testified that civil contractors hired to work in places like Afghanistan were not trained in interrogation techniques and were not given special rules allowing them to beat detainees.

The government is prosecuting Mr. Passaro under a provision of the USA Patriot Act that allows charges against American nationals for crimes committed on land or facilities designated for use by the government.