A second boy, 16, has been arrested after two acid attacks on delivery drivers, one of which has left the victim "fighting for his life".
The teenager is being held on suspicion of grievous bodily harm in relation to the assaults which took place in London in the space of half an hour.
A 14-year-old boy arrested on Friday has now been released under investigation.
Police said the victim of the first attack, a pizza delivery moped driver, was critically injured after being sprayed in the face with a corrosive substance and may lose his sight.
The 32-year-old was attacked in Walpole Road, Walthamstow, at about 6pm last Thursday, after being approached by two men on a moped who attempted to steal his vehicle.
He suffered severe injuries to his eyes and face, and also breathed in the noxious substance.
The suspects then fled on their moped as a member of the public went to the victim's aid, pouring water on his wounds.
The man remains in hospital in a critical condition.
Detective Chief Inspector Gordon Henderson, of Waltham Forest CID, said: "This attack has left a man fighting for his life and with terrible eye injuries.
"This was an innocent man going about his work as a delivery driver, who may never see again."
Appealing for information, he said: "Your phone call could save some other innocent person; it is imperative that we arrest those responsible."
Detectives are also investigating a second attack which took place half an hour later in Tottenham.
The second victim - also a 32-year-old delivery driver - was sprayed with a corrosive substance as two men on a scooter attempted to steal his moped.
He was treated in hospital for his injuries, but they are not believed to be life-threatening or life-changing.
Detectives are investigating whether the two attacks are linked.