When he was arrested last summer on suspicion of being a serial killer, Jeffrey L. Dahmer confessed to 17 slayings. Among his victims, he said, was a dazed 14-year-old Laotian boy whom he strangled at his apartment here only moments after three police officers had allowed the boy to remain in his care.

On Tuesday, two of those officers, both of whom were later dismissed for their handling of that incident last May 27, testified for the prosecution at Mr. Dahmer's insanity trial. The officers said Mr. Dahmer's reassuring manner and his photographs of the boy in bikini underwear had convinced them that the boy was not in any danger.

By Mr. Dahmer's own account, he had already drilled a hole in the boy's head when the officers, with a corpse of another victim lying in a bedroom only a few feet away, questioned him at his apartment. But the officers testified that the only noticeable injury had been a scrape on the boy's knee. Calm and Cooperative

The officers, Joseph Gabrish and John Balcerzak, had found the boy, Konerak Sinthasomphone, staggering naked on the street outside Mr. Dahmer's apartment. When Mr. Dahmer was questioned, they testified, he was calm and cooperative. "There was no reason to suspect anything at all," Mr. Gabrish said.