A drug dealer who plunged a “large, Rambo-style knife” into the chest of a drunk man before dumping the weapon in a river has been found guilty of murder.

Lee Crewe, 36, was stabbed to death in Chepstow Road in the Maindee area of Newport on 14 May.

David Sisman, of Hubert Road, Newport, admitted to killing the victim and to selling drugs that night, but denied murder.

But a jury at Newport Crown Court unanimously found the 21-year-old guilty on Friday.

Mark Cotter KC, prosecuting, told the trial Mr Crewe was “an unarmed and intoxicated man who was retreating” when the attack happened.

He said Sisman had given a no comment interview to police, adding: “If you were accused of murder and there was a true and simple explanation as to why you had driven a large knife into the chest of another man, well, wouldn’t you be telling police that?”

Tom Crowther KC, representing Sisman, said the attack had been self-defence, claiming he was protecting himself from Mr Crewe, who was “a roiling cauldron of boastful fury”.

Mr Crowther said a text sent by Mr Crewe shortly before he was stabbed read “I’m jacking somebody”, and said this made clear he planned to rob Sisman, as well as referencing the cocaine and alcohol the victim had taken.

He added his client pulled out the knife “in the heat of the moment” and instinctively stabbed Mr Crewe, “a much bigger man”, because he feared for his own safety.

But while Mr Cotter accepted Mr Crewe “may have been verbally unpleasant” when he approached Sisman in the street, he added being “a bit drunk and a bit aggressive because he wants to get his hands on some crack cocaine and he can’t pay for it”, did not suggest he physically threatened Sisman.

While Mr Crewe was dying, Sisman ran away, “heading to the hills” and dumping the knife in the River Usk, said Mr Cotter.

Judge Daniel Williams adjourned the case to November 28 for a pre-sentence report to be written and told Sisman: “The only sentence I can pass will be one of life imprisonment.”