A British man was found guilty on Wednesday of stabbing to death a teenage actor who played a small role in the upcoming film Harry Potter and the Half-Blood Prince.

18-year-old Rob Knox died after being stabbed five times outside a bar in Sidcup, Southeast of London, England in May 2007 as he tried to protect his younger brother Jamie, 17.

Rob Knox had a small part as Marcus Belby in Harry Potter and the Half-Blood Prince.

Karl Bishop, 22, was found guilty of his murder at London’s Old Bailey criminal court. He was also found guilty of wounding four of Knox’s friends during the violent altercation.

The court heard Bishop had been involved in a dispute with Knox at the bar the previous week. The following week he returned but was refused entry and ended up in another confrontation with Knox and his friends.

He returned home and armed himself with two kitchen knives. During the altercation Bishop threatened that he “would stab anyone who came near him,” prosecutor Brian Altman said.

Bishop showed no signs of remorse. When told that Knox had died, he replied: “Yeah, sweet.”

In his final statements, Justice Bean said, “You are at present a highly dangerous man. There is plainly a very significant risk to the public of serious harm caused by your committing further specified offences of violence. When you learned that you had killed Rob your only response was to say ‘Yeah, sweet’. Your lack of regret, let alone remorse, was truly chilling.”

Bishop was sentenced to prison on Thursday and told he must spend at least 20 years behind bars.

By Tessa Petrocco (Source: Variety/CNN)