Police have urged anyone who saw a couple “acting in an unusual manner” in the hours after a man was stabbed to death on a train to contact them.
Lee Pomeroy, 51, was knifed nine times at Horsley station in Surrey on Friday.
Detectives appealed for information about a man and a woman with a child seen in the Frensham Great Pond area, near Farnham, later that day.
Darren Pencille, 35, has been charged with murder. Chelsea Mitchell, 27, is charged with assisting an offender.
Mr Pomeroy, from Guildford, was attacked on the 12:58 GMT service to London Waterloo.
A post-mortem examination concluded he died as a result of multiple stab wounds, which included an injury to his neck.
‘Out of character’
Det Ch Insp Sam Blackburn, of British Transport Police, said the couple briefly stopped at a car park on Bacon Lane.
Appealing for anyone who may have seen them between 17:45 and 18:35 to contact officers, he said they would have been “acting in an unusual or out of character manner”.
They would have also been with a young child and arrived and departed in a blue Vauxhall Corsa, he said.
“If you were at the Frensham Great Pond car park during this time, please do get in touch as you might hold information which could help us uncover any new evidence,” he said.
Det Ch Insp Blackburn added that searches had been carried out in the Clandon area of Surrey and at a property in Bognor Regis, West Sussex.
Mr Pencille and Ms Mitchell appeared at Guildford Crown Court on Monday and were remanded in custody until the next hearing on 7 February.