ASHTON Kutcher is set to testify about the fateful night in 2001 when he found the brutally murdered body of his former love interest Ashley Ellerin.

Kutcher will be a critical prosecution witness in the case against alleged serial killer Michael Gargiulo with the star’s testimony key to establishing Ms Ellerin’s time of death the Daily Mail reports.

Mr Gargiulo, 32, of Santa Monica, faces two counts of murder and two counts of burglary in connection with the killings of 22-year-old Ms Ellerin, and Maria Bruno, according to prosecutors.

The actor has never publicly spoken about the gruesome incident, but is set to relive his nightmare when he takes the stand next year.

Kutcher was a 23-year-old in 2001 when Ms Ellerin, an aspiring model and student, asked him out on a date, but the actor turned her down.

Later that evening, Kutcher decided to make peace with Ms Ellerin and drove to her home in Hollywood finding the lights on.

According to reports, Kutcher knocked on her door before peeking in her window and seeing what he thought was red wine on the floor.

It was blood.

Kutcher didn't realise Ms Ellerin was already dead, having allegedly been stabbed 35 times.

Mr Gargiulo reportedly knew Ms Ellerin and took an intense interest in her in the time leading up to her death.

Read more about Ashton Kutcher's alleged serial killer nightmare at The Daily Mail.