Three young brothers who were abducted by their father are abroad and probably in mainland Europe, police believe.
The Met Police is now offering a £20,000 reward for information to find them and have so far made 15 arrests.
Cdr Bas Javid said he believed the children had been illegally taken out of the UK.
All three brothers were playing in the garden while their foster carer was inside the house in Coulsdon when they were taken on 20 August, detectives said.
Cdr Javid said they believed the father has used an illegal route to get the children out of the UK, possibly in a lorry as they did not have their passports with them.
Nobody has been charged, but the Met have released an image of a new suspect.
The man, described as bearded and wearing a stripy jumper, was seen in the passenger seat of a red Nissan Qashqai, at the time the children were taken.
“He may hold valuable information as to where the children and Imran are,” Cdr Javid said.
“We appreciate that the image is not the clearest quality but we still need people to really study it and see if the man in the picture is one that they may recognise.
“I can’t imagine how distressing this whole situation has been for the three young boys, who have been taken away from their safe environment, and our efforts to locate Imran Safi continues,”
It is understood the three brothers were up for formal adoption.
Cdr Javid added: “The investigative team has been working tirelessly on this case and we are appealing again because someone reading or seeing this knows there whereabouts of these innocent children and I need them to contact us urgently and provide that knowledge.”