Spray cans were found near the bodies of three men who have died after being hit by a train at a station in south London.
British Transport Police (BTP) officers were called to Loughborough Junction station, near Brixton, shortly after 7.30am after reports of multiple bodies being found on the track.
An investigation has begun to identify the men and the reason why they were on the tracks.
Officers were seen taking photographs of graffiti as part of their inquiries.
Detective Superintendent Gary Richardson, from BTP, said: My team are now working hard to understand what happened and how these three people came to lose their life on the railway.
My thoughts are with the family and friends of these three people.
At this time, we are treating their death as unexplained as we make a number of immediate inquiries. I would ask anyone who was near to Loughborough Junction this morning, and saw something which they think might be relevant, please contact us as soon as possible.
Sources told the Press Association that the incident could have happened overnight, when freight trains run, as the bodies were not spotted until around 7am.
There were no reports of any passenger trains being involved.
Mayor of London Sadiq Khan said: My heart goes out to the families of the three people killed at Loughborough Junction station this morning.
We are in close contact with the British Transport Police who are urgently investigating this incident.
Loughborough Junction station is between Herne Hill and Elephant and Castle and is served by Thameslink. The platforms and tracks are above ground level on a viaduct. The area is popular with graffiti artists.
National Rail said services would be delayed while inquiries continue.