Two men have died after collapsing in mystery circumstances at a sauna popular with gay men in central London.
Police launched a investigation after a third man fell ill at the Pleasuredrome sauna, near Waterloo train station, on the same evening.
Officers want to trace a man seen entering the adults-only Pleasuredrome, which is located under a railway arch, with one of the victims on Saturday night.
A 39-year-old man died at the scene on Saturday, while the second victim was taken to hospital, but died on Monday.
A third man received medical treatment in hospital and was later discharged.
IB Times contacted the venue, and was told it was again open for business. "It is safe," a spokesman said,
Police are awaiting the results of toxicology tests, because the cause of death could not be established.
The man sought by police is described as slim, aged between 25 and 35 years old, with a goatee beard.
A police spokesman said: "Officers have concerns for his welfare."
Anyone with information is urged to call the incident room at Lambeth police station on 0208 721 3597.