Harry Potter star's brother died after being turned into a "fireball" when he touched power line
Ben Haddon-Cave, 27, whose sister Jessie Cave played Ron Weasley's girlfriend Lavender Brown in the films, had been out drinking with 26-year-old Paddy Bolster who also died in the tragedy.
Both were electrocuted seconds after Ben took a photo of his pal as they jumped between containers on a freight train held at Hackney Wick station in east London, the inquest was told.
Ben's body was found on railway tracks a mile from where Paddy was found dead on top of a white cylindrical container after CCTV captured a "flash of light" just before 1am on Thursday March 21 this year.
British Transport Police Detective Constable Vicki Bladen, who played the video to St Pancras Coroner's Court, said shop staff had seen two figures go through the gates of an industrial estate next to the station that night.
She said: "There is quite a large hole in the fence.
"It's a dated industrial estate. The easiest way as the gate was open was to go through the gate and through the hole in the fence."
She replied "that's correct" after Senior Coroner Mary Hassell asked: "Your view is the area where the flash took place and the fireball is approximately adjacent to the gap in the fence where Paddy and Ben, it's believed, gained access having seen the CCTV of the two figures having come through the gated complex."
DC Bladen said: "At 00:54 hours or just after it will show a large flash of light and then it will show the train moving out of the station.
"As the train goes through Hackney Wick, we see what appears to be a body on the top of the white cylinder."
She replied "yes" after the coroner asked: "Is that person in the same position as photos showing Paddy when he was recovered?"
She added: "Following that you will also see what I would say is a fireball coming from what appears to be the top of the train.
"From that CCTV the fireball seems to be from the top of the train.
"When the London Fire Brigade came they obviously found the body of Ben.
"Paddy was found on top of that train, that ball of fire I believe that comes from the top of the train and I believe that ball of fire is actually Ben leaving the train and coming to land within the track area.
"I think at that time both of them were on top of the train."
She explained the pair used steps to climb on to an adjacent flat-bed container before jumping on to the white cylinder and Ben started taking pictures of Paddy.
DC Bladen said: "The last one is 00:54.
"There were photographs of Paddy. One of the photographs, it would appear, was on the top of the flat bed and one of the photographs, he was definitely on top of the cylinder.
"One of them was just before the flash."
Firefighters were called to the scene by a neighbour and police later declared the death as 'unexplained' at around 2.30am.
Ellen Robertson, representing Paddy's family, said "there was confusion" after DC Bladen said CCTV images from the station were not accessed until three hours later - minutes after Paddy was pronounced dead at 5.23am.
DC Bladen said: "There's procedures we need to go thorough.
"Of course we would have requested it but we are not in control.
"In an ideal world it would be great that we have direct access to the cameras but in this situation that's not the case."
Network Rail's barrister Alexandria Tampakopoulos told the inquest that Arriva, the company that runs Hackney Wick station, gave officers 'access' to the CCTV.
The inquest previosuly heard both men were in a state of "extreme drunkenness" when they climbed the trains.
Today pathologist Dr Alan Bates changed his original cause of death for Paddy to 'electrocution' after receiving reports of the incident from Network Rail.
Reading his report, the Coroner said: "It's been determined that approximately 1.30am Paddy was sighted on top of the freight train.
"At approximately 5.20am emergency services were able to access the top of the container.
"It's now apparent that Paddy did not fall from the train on the tracks which was the information that was given originally.
"The cause of death is most likely high voltage electrocution and occurred instantaneously as Paddy came into contact with or close to the live overhead line."
Ben was born in the capital and lived in Clerkenwell, central London, near his family.
Paddy was a third-year student in countryside management and conservation at Aberystwyth University and grew up in County Cork, Ireland.
Ben's pal of seven years was a student at Aberystwyth University and had come to London that afternoon to go to a comedy show.
Ben also worked as a music producer and an actor who was expected to play the lead role in an upcoming film.
His other sister Bebe starred as Wilhelmina Coke in ITV's historical drama Victoria.
Ben's family said in a statement: "The very last thing he said to Jamie, who was also at the gig but had to leave early, was he loved him - something he would often say to all of us.
"In our view, stepping onto that freight train that night was an out of character decision.
"We believe that he has been depicted as some sort of reckless train surfer but that could not be further from the truth.
"He was a profoundly talented and creative mind."
The family said he had gone to the prestigious Lambda and the Rada drama schools and was planning to play the "lead role in an upcoming short film and some advertising work."
Paddy's mother Tara Bolster said: "Losing my son in these circumstances has been devastating.
"But what tortures me everyday is playing over and over in my head different scenarios of what might have happened that night, and wondering if anything could have been done to save Patrick.
"It took around 30 minutes before Patrick was even spotted on top of a train and, even then, he was left there for hours until he was finally tended to.
"Knowing that, I'm dismayed that Network Rail didn't cut the power to the overhead lines for almost four hours, which finally enabled emergency services to reach Patrick.
"There will always be a lingering doubt in my mind that Patrick could still be alive had he received medical treatment immediately."
Tara's solicitor, Tracey Benson, a personal injury lawyer at Slater and Gordon, said: "Throughout the inquest we've heard details of confusion in the aftermath and delays in responding.
"This has added to the family's trauma and provoked more questions.
"They want to know that everything was done to try to save Patrick - they've been left with very grave doubts that was the case."
The inquest continues.