Three men have been arrested by detectives hunting the killers of a have-a-go-hero.
Sukhwinder Singh, 31, died from a stab wound to the heart after he confronted the robbers in Barking, east London.
He chased the men after witnessing them rob a 28-year-old woman of her handbag as she was walking home from Barking station.
A Met Police spokesman said the three suspects were arrested at about 2pm on Wednesday and are currently in custody at a police station in east London.
Detective Chief Inspector Stephen Clayman said: "We need to hear from anybody who witnessed the initial robbery, the actual stabbing and anyone who may have seen suspects running away from the Uphall Road area, or perhaps discarding property in the vicinity.
"I wish to encourage members of the public to come forward and speak to police - no matter how insignificant they may feel their information is. If they have fears regarding speaking to police, I assure them that we can allay those fears."
Police were called to Uphall Road, at the junction with Victoria Road, shortly after 7pm last Friday.
They found Mr Singh, of Harts Lane, Barking, with a serious injury. He was taken to the Royal London Hospital where he was pronounced dead. A post-mortem gave the cause of death as a stab wound to the heart.
Police said the robbery victim was attacked from behind as she walked in nearby Loxford Road.
Mr Singh chased the suspects for some 50 to 70 yards along Victoria Road into Uphall Road, where it is believed an altercation took place.
