Pencille, a violent felon with a long criminal record, was sentenced to not less than 28 years for stabbing Pomeroy 18 times in front of his 14 year old son.
"Lee Pomeroy was travelling with his 14-year-old son when he was "savagely" stabbed 18 times by Darren Pencille on the Guildford to London service.
Mr Pomeroy died with his son next to him at Horsley station on 4 January, the day before his 52nd birthday.
Pencille killed the father-of-one when a "chance encounter" escalated into a frenzied and fatal attack, the court heard.
He first stabbed the IT consultant in the neck, then inflicted 17 more injuries in the 20 seconds that followed."
"Mr Pomeroy and his son got into the same carriage as Pencille at London Road, Guildford, and made their way down the aisle before the row started.
Jurors heard they may have been blocking Pencille's way, prompting him to make the remark: "Ignorance is bliss."
The row escalated into swearing as Mr Pomeroy demanded an apology, but then Pencille produced a knife and stabbed him in the neck, cutting through the jugular vein.
The court heard Pencille, who declined to give evidence during his trial, had 14 previous convictions for 19 different offences over a 19-year period, including possession of offensive weapons, violence and dishonesty.
In 2010, he had stabbed a flatmate in the neck over a minor disagreement."