Officers have been examining CCTV footage near the depot where two suspected graffiti artists were killed by a London Underground train.
Forensic scientists examined the scene near Barking station
The pair, aged 19 and 21, were hit by a District Line train at the Barking depot in east London late on Friday.
A security guard saw a group spraying graffiti nearby just before the crash.
Two men, aged 25 and 23, who were arrested on suspicion of causing criminal damage, have been released on bail by the police.
The victims were pronounced dead at the scene and their bodies were moved from the tracks early on Saturday morning.
Although both victims have been identified, police said they would only be officially named after both their families had been informed.
Officers began an investigation after the deaths at about 2300 GMT on Friday night.
They have been looking at CCTV images and speaking to witnesses, and forensic scientists have carried out a scene examination.
Ch Supt Paul Crowther said although vandals were spotted by a guard, they had not been chased.
He added that the incident was a reminder that spraying graffiti near railway lines was a "dangerous pastime".
Local resident Jon Leitch said: "It was absolutely horrendous seeing the bodies right outside your window and especially when you think they are someone's relations that won't be returning home.
"It's not worth paying that sort of price to spray graffiti."
Another resident, Aitee Odie said a two-metre fence topped with barbed wire surrounded the Barking station but people still managed to get on the tracks.