Mr Gregory, from Charlton, had been out celebrating the festive season with friends at The Earl of Chatham pub on December 23 when Nguyen lashed out at him with a glass in the toilet, slashing the arteries in his neck.
The horror attack appeared to stem from a trivial incident at the bar a short time earlier where the pair exchanged words.
The killer told his offender manager he would have walked away from the situation if he was sober – “it’s the drinking,” he said.
Nguyen, now aged 50, was first released from prison on licence in October 2022 but was recalled four months later for breaches related to alcohol.
He was then released again in March 2024, before being recalled a second time in January this year after it was alleged that he consumed alcohol throughout the Christmas period.
The reasons for recall stated: “You have been warned for a notice that you had an alcohol violation. Following this warning your alcohol monitoring device detected further alcohol use.
“Given that alcohol is a direct link to potential for violent behaviour and serious offending your risk cannot be managed within the community at this time.”
Nguyen challenged the recall decision at the High Court of Justice last month.
He denied consuming any alcohol and asserted that the electronic alcohol monitor must not have been working properly.
However, High Court judge Vikram Sachdeva KC dismissed his challenge, stating there was sufficient evidence that he had been consuming alcohol.
Mr Sachdeva said: “The combination of the breach of the alcohol monitoring tag on three occasions, his history of committing a serious violent offence whilst under the influence of alcohol, the risk to the public being assessed as high, and the judgment that he was not now taking responsibility for alcohol use, the defendant was entitled to find that the safety of the public would be at risk if the claimant remained on licence.”
