Grieving family members are pleading with anyone to come forward with video footage of a man possibly being abused by bouncers at a gay-friendly club.
Police have issued the appeal following the death of 30-year-old Adam Hird, who died following an incident outside a bar in Vauxhall.
Detectives investigating believe a woman may have filmed the events on her mobile phone. A cash reward of £1000 is available ($1700, €1300).
In the early hours of Sunday 15 June, the aspiring pilot engaged to a woman was left unconscious after the alleged confrontation outside Club No 65 in Vauxhall, a venue south of the River Thames directly next door to gay sauna Chariots.
Officials were called at 3.20am to reports of a male being restrained by security staff at the entrance of the bar.
On arrival, they found Hird had collapsed. He was taken to hospital where he died on 17 June.
A post-mortem examination has taken place, with results of further tests waiting to be revealed.
A tall woman in her 20s, with blonde hair in a ponytail, wearing shorts, is believed to have filmed the incident on her phone.
Police are keen to secure any footage of the incident, and are asking her to come forward.
‘I would like to reassure this woman that she is not in any trouble and that she can contact the police with the confidence that she will be treated with the utmost sensitivity,’ Detective Inspector Sharon Marman said.
A statement from Hird’s family have described him as ‘full of life, kind, gentle and funny’.
They said: ‘We never imagined that this could happen, right here, so close to where we live, where he should have been safe. We are deeply shocked and distraught at what has happened to Adam’
Four men, three in their 20s and one aged 50, were arrested at the scene on suspicion of assault.
Following the incident No.65 bar on Albert Embankment has been closed and is likely to remain closed until further notice.
Anyone who witnessed the incident is asked to call +44 (0)20 8721 4051, or to remain anonymous call Crimestoppers on 0800 555 111.