Melvin Theuma was due to give evidence in the case on Wednesday, but was found in his police-protected residence the night before with stab wounds.
A self-confessed middleman in the murder of Maltese investigative journalist Daphne Caruana Galizia has been found with stab wounds in his police-protected residence the night before he was due to give evidence at trial.
Melvin Theuma is currently being treated in Mater Dei hospital after suffering "serious injuries" that a preliminary investigation found to be self-inflicted, police have said.
Local reports, meanwhile, said the former taxi driver had been found on the floor of his bathroom with his throat slit and a wound to his abdomen.
Theuma was due to appear in court on Wednesday to give evidence over the assassination of Caruana Galizia, a prominent anti-corruption journalist who was killed when a bomb was detonated inside her car in October 2017.
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He had earlier been given a presidential pardon in exchange for him giving details on how the assassination was planned.
But on Tuesday evening, police said Theuma's lawyer raised the alarm after she was unable to contact her client.
Officers stationed round-the-clock outside his residence then entered the building with his wife to find him with his injuries.
An investigation is now ongoing into the incident and a Magisterial Inquiry has been requested.
Local media have widely reported that Wednesday's court hearing was expected to be a pivotal moment in the case to convict Caruana Galizia's killers.
Theuma has previously claimed that he acted as a middleman in the crime by contracting three men to carry out the act on behalf of Maltese businessman Yorgen Fenech.
The gambling tycoon was later arrested and charged with participating in a criminal organisation, complicity in causing an explosion, and complicity in the murder of Caruana Galizia.
He has pleaded not guilty to all the charges.