Dozens of police hunting the Clapham chemical attacker raided a flat in east London where it is believed the suspect's brother lives - evacuating shocked neighbours and questioning them at 2am.
An officer told residents: "We are looking for someone. It's not safe to be in there, just in case there's a hazard we need to know about."
Police have named Abdul Ezedi as the man they are hunting after a woman and her two daughters had a corrosive substance thrown over them in Clapham, south London, on Wednesday night.
The suspect is thought to have been seriously burned during the attack before he fled.
Police asked residents in the flats they raided early on Friday in east London: "Have you seen a man with an injured eye?"
In an audio recording of the raid obtained by Sky News, officers can be heard waking up residents and ordering them to leave the small block in Leytonstone.
One says: "Show me your hands. How many of you are there? Come out slowly, put your hands on your heads and walk toward me. One by one, move to your right and keep going.
"We are police officers and we have a search warrant for this address. We are looking for someone. It's not safe for you to be in there."
Residents were questioned in police cars parked nearby and were later let back into their flats. It is thought the suspect's brother was among them, but he claimed to have had no recent contact with him.
Video footage obtained by Sky News shows dozens of police earlier preparing for the raid, dressing in protective suits and gas marks at a police station a few miles from the flats.
Police, fire officers and ambulance crews drove in convoy to the address off Leytonstone High Road.
They set up decontamination showers in the road outside the building, but it is thought they found no corrosive substances.
Damage was later visible on the door to the block of flats where police had forced their way in.