Ashton Kutcher has told a court how he "freaked out" when he discovered that his date had been stabbed to death in her home 18 years ago.
The 41-year-old told the trial of alleged killer Michael Gargiulo how he turned up late for a planned date at fashion designer Ashley Ellerin's Hollywood home in 2001.
When she did not answer the door, the film and TV star said he had looked into the window and saw what he first believed were wine stains on the carpet.
He assumed he had "screwed up" by turning up two hours late and left.
But he discovered the next day that she had been killed and that the stains were blood.
Prosecutors say Ms Ellerin, who was found by her housemate, had been stabbed 47 times.
Giving evidence at the trial on Wednesday, Kutcher said he knew his fingerprints were on the door and was worried about what police would think.
He told the court: "I remember the next day after I heard about what happened, I went to the detectives and said 'My fingerprints are on the door'. I was freaking out."
Kutcher is now a father of two married to actress Mila Kunis. He was previously married to Demi Moore.
Describing going to her house, he said: "I knocked on the door and there was no answer. I knocked again, and once again, no answer. At this point I pretty well assumed she had left for the night, and that I was late, and she was upset."
He said he did not arrive at her house until about 10:45 p.m. He called her in the interim four times and could not reach her but assumed it was bad phone service.
"Eighteen years ago, cell service wasn't it what it was today," he said.
He said he did not leave messages every time he called. "I was trying to take her on a date and didn't want to seem eager," Kutcher testified.
The former Two and a Half Men star was testifying as a witness at the trial of Gargiulo, who is accused of murdering Ms Ellerin and another woman.
The 43-year-old is also accused of the attempted murder. He is charged separately with killing an 18-year-old Glenview, Illinois, woman, and is awaiting trial there.
Prosecutors say the attacks took place in the Los Angeles area between 2001 and 2008.
Gargiulo, who was arrested in 2008, has pleaded not guilty at Los Angeles Superior Court.
The trial continues.
