The court heard evidence that both men had been drinking at a party before getting into Mr Cuthbert's orange Chevrolet ute in the early hours of February 15, last year.
The ute was travelling at between 90 and 100km/h in a 50km/h zone in Glen Eden when it crashed into a retaining wall.
The ute flipped and Mr Cuthbert was flung from the vehicle and pinned underneath.
He died at the scene from severe head injuries. Watson was able to get himself free from the wreck.
Police tests found Mr Cuthbert and Watson to be 2 times over the legal alcohol limit for driving.
Justice Patrick Keane summed up the case yesterday and told the jurors: "Focus on the issue, the only issue, who was the driver?"
Crown prosecutor Brett Tantrum told the jurors that although no one saw the crash, they could draw inferences from the evidence.
He said witnesses first on the scene saw Watson sitting "close to the driver's side" of the ute.
Mr Tantrum said forensic crash expert Professor John Raine said the person in the driving seat was protected by a pillar and the steering wheel and would have been less likely to have been injured.
Mr Tantrum said the professor described the crash as needing the "perfect storm" of circumstances to get the driver in the position where Mr Cuthbert was found.
He also quoted Crown witness Danny Rea who told the court that Watson had admitted to being the driver. Outside court, Mr Cagney said his client was a changed man since the crash. "He's been dry for 17 months."
Watson will be sentenced in October.
