The driver of a train which fatally dragged a dog along a station platform did not know its lead was trapped in the doors, an investigation has found.
Disabled pensioner Rose Barry was struggling to board the Thameslink service at Elstree and Borehamwood station, Hertfordshire, on September 7 last year when the accident happened.
The 75-year-old retired nurse was trying to enter the train with her Shih Tzu dog named Jonty, walking frame and luggage when the doors closed, trapping her hand.
She was able to pull herself free but the lead was stuck in the doors, resulting in Jonty being dragged when the train departed.
The dog was subsequently found dead in a tunnel near the station.
An on-train CCTV system allows drivers to view the side of the train and the adjacent platform during the dispatch process.
But the Rail Accident Investigation Branch (RAIB) stated that the driver said he had "no recollection of seeing the passenger or her dog in the monitors".
An inspection of the recorded CCTV images found that Ms Barry was "clearly visible, standing in close proximity to the train", the report found.
The RAIB highlighted that the driver carried out his final safety check before departure in no more than 1.1 seconds.
This is compared with the 13.5 seconds recommended by the Rail Safety and Standards Board (RSSB) to ensure a "full and safe inspection of the CCTV images" takes place.
The design of the train's system which detects obstacles stuck in the doors is unable to detect thin items, meaning the train was able to depart with the dog's lead trapped.
The RAIB made a safety recommendation to Govia Thameslink Railway - which owns the Thameslink franchise - relating to the time drivers spend carrying out safety checks.
It also urged the Rail Delivery Group, which represents train companies, to investigate technologies which improve the detection of people or items trapped in train doors.
Ms Barry, who has back problems, told the Press Association at the time of the accident: "It was terrible.
"There is a curve in the platform and either the driver couldn't, or failed to, look at the CCTV.
"He should have been able to see me standing there, half on the train.
"Obviously he didn't because the doors shut and he left immediately. There was no hesitation.
"I hammered the doors (and) yelled at everybody."
GTR head of safety Mark Whitley said: "This was a deeply upsetting incident and we are very sorry for the distress caused to the dog's owner.
"As well as informing the Rail Accident Investigation Branch when it happened, we launched our own investigation immediately and have already introduced new guidance to drivers about the optimum time needed before departing, in line with the Branch's recommendations.