The following appeal was featured on tonight's BBC One Show (Thursday, 19 October)
Detectives in Croydon are re-appealing for information and witnesses after two women were robbed at knife-point of their gold necklaces in Thornton Heath.
The women, aged in their 60s, were approached by four men riding on two mopeds in Bensham Manor Road, on 20 September at around 15:09hrs.
During the incident the pillion passengers got off the bikes and threatened the victims with a knife, before snatching a total of four gold chains from the victims' necks.
A male witness, aged in his 70s, attempted to intervene and was thrown to the ground by one of the suspects.
The suspects then made off on the mopeds towards White Horse Road.
London Ambulance Service attended the scene. The witness who intervened was taken to a south London hospital with a minor head injury. He was later discharged.
There have been no arrests and enquiries continue.
The suspects are described as three white males and one black male. All four wore motorcycle helmets.
Any witnesses or anyone with any information is asked to call Croydon CID on 101 or contact the Met via Twitter @MetCC.
To give information anonymously contact Crimestoppers on 0800 555 111 or online at crimestoppers-uk.org.