Newcastle chemical attack suspect Abdul Ezedi may have taken his own life or be using an ally to stay hidden, a former senior police officer has said.

Metropolitan Police officers have been searching for the 35-year-old since Wednesday after a 31-year-old woman and her daughters, aged eight and three, were attacked in Clapham.

The woman, who suffered potentially life-changing injuries, was known to Ezedi and remains in hospital in a critical but stable condition.

The manhunt entered its fifth day on Monday with a £20,000 reward in place for anyone with information leading to his arrest.

Nick Aldworth, a former national counter-terrorism co-ordinator, told BBC Radio 4’s Today programme: “I think if we’ve not seen or heard from him in the the last couple of days, which appears to be the case, he’s gone to ground, possibly supported by somebody… or it’s not unlikely or improbable that he may have taken his own life. There is therefore a body to be found somewhere.”

Mr Aldworth said the Met would be tracking Ezedi’s movements through public cameras, which had been a “very effective” method in previous cases.

The force said the last sighting of Ezedi, who is from Newcastle, was at 9.33pm at Tower Hill Underground station in east London on January 31, shortly after the attack in Clapham.

Asked if the Met Police would now have a precise location for his whereabouts, he said: “I think they’ll have a very good sense of what area he’s in.

“What you can’t discount of course is that he has been picked up by an ally and moved somewhere else, perhaps in a vehicle. The reason they’ve offered a £20,000 reward is usually because there’s a sense that somebody inside the community might well be harbouring this individual.”

On Sunday, police said the suspect used a “very strong concentrated corrosive substance” – thought to be alkaline – in the attack.

Police investigators believe there are people who know Ezedi’s whereabouts and have not come forward.

The Met has warned anyone found assisting him will face arrest.

It comes as questions have been raised over how the suspect, who was granted asylum in the UK after two failed attempts, was able to stay in the country despite being convicted of a sex offence.

Downing Street said the Government had already taken action to stop people trying to “game the system” but was unable to comment further on a live police investigation.

Police said Ezedi left Newcastle in the early hours of Wednesday and travelled south to London and was in the Tooting area by around 6.30am.

His vehicle was seen again in Croydon, south London, at around 4.30pm and by around 7pm he was in Streatham.

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Ezedi allegedly threw the younger child to the ground during the attack at 7.25pm, before attempting to drive away from the scene, crashing into a stationary vehicle and fleeing on foot.

Minutes later he boarded a Tube train at Clapham South Underground station, and by 8pm he was at King’s Cross Tube station.

Police say three members of the public who came to the aid of the family during Wednesday’s attack, two aged in their 30s and one in her 50s, have all been discharged from hospital with minor burns.