Police investigating the murder of Lee Pomeroy have been given another 12 hours to question his suspected killer.
The extra time will also be used to question a 27-year-old woman accused of assisting an offender.
The extension follows the arrest of the 35-year-old murder suspect and the woman a flat in Farnham on Saturday morning.
Police said Mr Pomeroy, a married father-of-one from Guildford, had been on a trip to London with his son on Friday afternoon when he was stabbed to death in a "horrific and pointless attack".
The family of the father, who would have turned 52 on Saturday, described him as "an honourable man" who "would always help somebody who was in trouble".
Paying tribute, his family said in a statement on Saturday: "Lee took his son on a trip to London hoping to spend some quality time with him, which was cut short by a 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."
Mr Pomeroy was pronounced dead in the carriage at Horsley station after suffering multiple stab wounds in what police have described as a "violent killing". The attack took place on a train travelling between Guildford and London Waterloo.
Police have sought to reassure the public, saying they do not believe the attack was random.
British Transport Police Assistant Chief Constable Sean O'Callaghan told Sky News the men joined the train at Guildford and a discussion occurred between them on the train.
"That continued for between three and four minutes," he said. "During the course of that discussion, both men moved to a second carriage, and that is where the violence ensued to the ferocity that we are now aware of and tragically that is where the man lost his life."
DCI Sam Blackburn, also from British Transport Police, said: "The investigation is moving with good progress and we are now 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 ongoing investigation."
The attack happened on the 12.58pm service travelling from Guildford to Waterloo. Officers were called to Horsley station at 1.15pm.
The victim's family, including his teenage son who was nearby at the time of the attack, are being supported by police officers.
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A post-mortem is scheduled for early next week.
Police are still appealing for anyone with information about the stabbing to come forward.