A train driver dragged a dog to death because he did not realise the animal's lead was trapped in the door - while the dog stood on the platform .
Retired nurse Rose Barry looked on in horror as the train doors closed as she was trying to board, trapping her dog's lead and her belongings inside the carriage.
But instead of checking his mirrors, the driver pulled out with eight-year-old Shih Tzu Jonty still stuck, pulling it along the platform to its death.
Investigators looking into the incident, last September, discovered the 75-year-old had been wearing a long scarf, which came dangerously close to her being pulled to her death with her pet dog.
CCTV of the event from September revealed the dog's lead becoming trapped as the doors closed on the departing train.
Panicked, the woman tried to raise the alarm by waving her arms and shouting - but the train pulled off into the distance.
According to The Rail Accident Investigation Branch (RAIB), the driver missed the passenger on his onboard train cameras.
The woman had been 'standing close' to the train when he decided to close the doors before it was safe to leave the station.
Modern trains include an obstacle-detection system, but a thin object, such as the lead, wasn't picked up by the sensors.
The RAIB recommended that Govia Thameslink Railway develop guidance on what time drivers should close their train doors.
It was also suggested that their onboard technologies were investigated to 'better assist train staff to detect people or items'.
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A spokesman for the RAIB said: "At around 2.03pm on Friday, September 7, 2018, a passenger and her dog were involved in a train dispatch accident at Elstree and Borehamwood station.
"As the passenger was boarding the train, the doors closed trapping her dog's lead, while the passenger and the dog were left standing on the platform.
"The train then departed, dragging the dog off the platform and into the gap between the platform and train. The dog suffered fatal injuries.
"The passenger was not physically injured but was very distressed by the accident. In slightly different circumstances, the passenger herself could have become trapped by the long scarf she was wearing."
He added that the driver has been operating trains on the Thameslink route from Bedford into central London since 2003.
Govia Thameslink Railway has been contacted for comment.
