The 24-year-old Culkin confidently rejected suggestions that he might have been molested during his sleep without knowing about it and dismissed a prosecution display of sex magazines seized from Jackson's home, saying he used to keep Playboys under his own bed.
When defense attorney Thomas Mesereau Jr. asked Culkin if he was ever molested by Jackson, he replied, "Not at all."
"I don't think that jurors believe celebrities more than the rest of us, but I do think that jurors pay more attention when a celebrity is on the witness stand," notes CBS News Legal Analyst Andrew Cohen. "So I think the defense message of the day -- that Jackson was quite capable of keeping his hands off young boys -- probably got through clearly."
The actor's testimony was followed by a key decision in which the judge allowed the defense to play a videotape in which Jackson spoke of his love for children. The jury heard Jackson say, "They need to be held and loved and told somebody cares."
Culkin was the third young man to testify at Jackson's child molestation trial that as boys they slept with Jackson at his Neverland ranch and weren't molested.
Culkin testified that he and Jackson were drawn together by their common experience as child performers, although he laughingly noted that "it was not like a child actors' self-help group."
"Anyone who was a child performer," he said, "we keep an eye out for each other."
Jackson, 46, is accused of molesting a 13-year-old boy in 2003, giving him wine and conspiring to hold the boy's family captive to get them to rebut a documentary in which Jackson told an interviewer he let children sleep in his bed but it was innocent.
Culkin became part of the case when prosecutors were allowed to present testimony to suggest Jackson has a pattern of abusing boys. The testimony included an ex-chef who said he saw Jackson with a hand up Culkin's shorts as Jackson held the boy up to a video game.
Culkin appeared relaxed and answered questions directly during less than 90 minutes of testimony. Godfather to two of Jackson's children, Culkin has appeared in such Jackson productions as his "Black or White" music video.
Culkin testified that he was 9 or 10 years old when he met Jackson and that he slept in Jackson's bed several times between the ages of 10 and 14, sometimes with other boys as well. He said the sleepovers weren't planned and that he and others would just fall asleep when they were tired.