A father-of-five made a desperate call to police just moments before he was stabbed in a Lancashire park.
Mr Shafiq called the police before trying to stop the fight
Mohammed Raja Shafiq was trying to stop a fight in Thompson Park, Burnley, on Tuesday when he was stabbed and hit with an iron bar. He died hours later.
Police admit they are "concerned about how Mr Shafiq was dealt with" and have referred the matter to the Independent Police Complaints Commission (IPCC).
Four males, aged 20, 19, 19 and 16, are being held on suspicion of murder.
A 17-year-old is also being questioned on suspicion of violent disorder.
A spokesman for Lancashire Police said: "We can confirm that a phone call was received from Mr Shafiq during the afternoon of Tuesday, 4th March.
"A review of that call and our response to it has caused us some concern and this afternoon we have referred that element of the investigation to the Independent Police Complaints Commission (IPCC)."
Detectives are investigating whether the fight in the park was related to an alleged attack on Mr Shafiq's son five months ago.
Mr Shafiq was hit on the head with an iron bar and stabbed
According to police, about 10 people were involved in the fight but up to 50 others watched.
Mr Shafiq, 50, of York Street, Nelson, was hit on the head and stabbed in the abdomen during the fight. He was taken to the Royal Blackburn Hospital where he later died.
A lake in the park has been drained in an attempt to find the weapons used in the attack.
Mr Shafiq's son is believed to attend Burnley College, which backs on to the landscaped park.
A pupil from Burnley College said he thought the victim's son had got involved in an argument and that his father had intervened.
Police have cordoned off a grassy, flat bank next to the boating lake and forensic teams were at the scene on Wednesday night.
Family friend Shokat Malik, 42, from Burnley, said: "His son had phoned his father and said there was a gang of youths bullying him so his father rang the police and then made his own way over there as well."
Police are urging anyone with information about the attack to contact them.