A woman had to be taken to hospital after she sat on a bench at a bus stop and was badly burned because someone had put acid on it.
The woman's skin and clothes were burnt.
Police want to speak to two men captured on CCTV on a bus who they say were "fiddling with a plastic bag and bottle".
The men got off the bus in Feltham, south west London just before 2pm on April 28.
The then walked to the bench and took something out of a blue plastic bag.
A short while later a woman sat on the seat and said there was a "sticky substance" which had burned through her clothes onto her skin.
She was taken to a hospital in west London and treated for burns. Police say they believe it was a form of acid.
Officers late found the bus the men were travelling on and found burn marks on the fabric of the seat and floor where they were sitting.