A second man from Wolverhampton suspected, in connection with the acid attack on a three-year-old boy in Worcester, remains in custody.
A 39-year-old man from Wolverhampton who was arrested on Sunday also remains in custody after Saturday’s attack in Worcester, which left the three-year-old with burns to his face and arm.
Meanwhile, officers are continuing to question three men from London aged in their 20s who were arrested early on Monday on suspicion of the same offence.
Detective Inspector Jim Bayliss said: “Our officers are continuing to work extremely hard on this investigation.
“At this time we believe this to be an isolated incident and there is not a wider risk to the public.”
Police have sustained working to ensure the safety and security of the victim and his family as they recover from their “shocking” ordeal on Saturday at a Home Bargains shop near Worcester’s Shrub Hill railway station.
The child injured in the incident was discharged from hospital on Sunday after treatment however, the long-term implications of his injuries are as yet unknown.
Police also moved to dismiss reports that there remained a racial motive behind the attack.
Chief Superintendent Mark Travis said there were believed to be no links among the incident and an English Defence League (EDL) march held nearby on the same afternoon.
Mr Travis said: “I would like to reassure people both nationally and within Worcestershire that instances of this nature are very, very rare.
“I would like to be very, very clear – there is no evidence to suggest that in any way this incident is motivated by race or anything to do with the EDL protest.”
Mr Travis added: “We are in touch with the family – the family are being supported by specialist officers.
“Clearly it’s a difficult time for them – they are coming to terms with something that is quite shocking.”
Officers have declined to confirm the ethnicity or nationality of the family and have said they will not issue any further information regarding their identities.
Mr Travis said officers had taken possession of CCTV footage and believed that the boy was targeted.