The father murdered on a train in Surrey in an "horrific and pointless attack" had been taking his son on a trip to London, his family have revealed.
In a statement released on what would have been his 52nd birthday, they said Lee Pomeroy was "an honourable man and would always help somebody who was in trouble".
The statement was released as police continued to question a suspect arrested in a dawn raid on Saturday in Farnham.
Mr Pomeroy was travelling with his 14-year-old son on the 12.58 service between Guildford and London Waterloo on Friday when he was stabbed several times.
His family's statement, released through British Transport Police, said: "Lee took his son on a trip to London hoping to spend some quality time with him which was cut short by an horrific and pointless attack.
"Lee would have had his birthday today but did not get to see his presents.
"He was an honest, bright person, who loved music very much. He knew history and art and he was a bachelor of science in maths.
"He was a devoted family man and did everything for his family.
"He was an honourable man and would always help somebody who was in trouble.
"He was a loving husband and father. He will be deeply missed by all his family."
BTP said Mr Pomeroy's family were appealing for privacy as they come to terms with their loss.
The suspect was detained at around 6am on Saturday on suspicion of murder. A 27-year-old woman was also arrested on suspicion of assisting an offender.
BTP said no-one else was being sought in connection with killing.
Detective Chief Inspector Sam Blackburn said officers were "confident to say that this is not believed to be a random assault.
"In the moments leading to the violent killing, both men appeared to be involved in an altercation lasting three minutes.
"Nothing justified the extraordinary violence that followed and we are concentrating our efforts on the on-going investigation."
BTP Assistant Chief Constable Sean O'Callaghan said no-one else was being sought in connection with killing.
He said: "We now know from inquiries we've been doing overnight and from witnesses that the two men were involved in a verbal discussion, that discussion lasted three to four minutes, it moved through one carriage from where they first boarded into another carriage, and that argument escalated to the unprovoked violent attack that sadly resulted in the death."
Mr Pomeroy and his son boarded the train at around 1pm at London Road station in Guildford.
A dedicated team of detectives and search officers have been working tirelessly throughout the night alongside @SurreyPolice.
Our thoughts remain with the family of the victim, including his 14-year-old son who was nearby when the assault happened.
— British Transport Police (@BTP) January 5, 2019
The killer, described as a black man in his 20s to 30s, approximately 6ft tall and of slim build with a beard, also boarded the service at London Road.
Police say the knifeman left the train at Clandon station and headed in the direction of Dedswell Drive. The train continued to Horsley station where police and paramedics attended.
A woman who lives in Clandon reportedly told other villagers that she had spoken to a "very sweaty and nervous" man in a field near her home afterwards.
Philip Herrington, the Rector of St Mary's Church, West Horsley, visited Horsley train station on the afternoon of the attack and the following morning.
"I thought I'd come and bring some flowers because you don't really expect anything like this to happen generally, not in a place like this, not on a midday train," Mr Herrington said.
"It's totally lamentable what happened and particularly for the young son to have witnessed what he witnessed."
Mr Herrington spoke to British Transport Police at the scene of the incident on Friday and offered assistance to passengers.
He said: "British Transport Police officers were pretty shocked at what they'd seen as well."