Actor Gravelle plays Tom in the series and is best known for his portrayal of shady suspect Joe Miller in ITV crime drama Broadchurch.
He had a major role in both seasons one and two opposite Oscar winner Olivia Colman who played his unsuspecting police detective wife.
The star has also featured in the hit Welsh BBC drama Keeping Faith as Terry Price and
Some of his other notable roles are in Channel 4’s The Accident, the Widow, and Unseelie Jack in Amazon’s fantasy extravaganza Carnival Row.
In more recent years, Gravelle has starred in the TV series Curious Under the Stars, The Snow Spider, Exile and Manhunt.
As well as being an actor, he is also an animator and lecturer based in Cardiff.
Silent Witness continues on BBC One tonight at 9pm