Three boys are being questioned by police following the death of a 57-year-old fisherman in Bedford on Wednesday afternoon.
Police said the boys, aged 12, 13 and 15, are in custody in relation to a potential assault on the man.
Josip Jovanovic, 57, of Bedford, had been fishing at the town's Embankment.
A pathologist said Mr Jovanovic's death was not caused by injuries sustained in the incident but that more tests would be carried out on his heart.
Mr Jovanovic became involved in a confrontation with a teenage boy who is believed to have tried to steal his bike, a police spokesman said.
The boy ran away without the bike but Mr Jovanovic collapsed a few minutes later.
"He was taken to South Wing Hospital where he died later in the afternoon.
"He has three adult daughters, one living in Bedford, and a partner."
Police say the family was being supported by family liaison officers.
They said the case was not being treated as murder.
Detectives are keen to hear from anyone who saw anything suspicious in the Embankment area around 1439 BST on Wednesday.
Correction 20 August 2010: An earlier version of this story suggested police were not connecting Mr Jovanovic's death to the confrontation with the boys. In fact police said a post mortem examination showed he did not die of injuries sustained in the incident.