A barrister for Avinash Treebhoowoon was outlining to the jury his client's claims that he was forced to sign a confession when John McAreavey spoke out from an otherwise silent public gallery.
"Lies," he said audibly.
Sanjeev Teeluckdharry had told the Supreme Court in Port Louis, Mauritius, that Treebhoowoon had been wrongly accused of the crime and subjected to torture.
Treebhoowoon, 31, and Sandip Moneea, 42, deny strangling the daughter of Tyrone Gaelic football boss Mickey Harte in the luxury Legends Hotel on the holiday island last January.
Mr Teeluckdharry did not react to Mr McAreavey's interruption, which came at the close of his address.
The lawyer had been telling the court that his client would enter the witness box and tell jurors how he was treated by police.
The trial continues.