The incident took place at the Ickenham station, which is treated by the Piccadilly and Metropolitan lines, in western London at 10.30 pm on March 28.
After falling on the track, the pin was hit by a train before being discovered by the personnel of the London Metro station.
The pin suffered fatal injuries as a result of the incident.
Today (April 16), the Railway Research Branch (RAIB) launched an investigation into death.
The agency said that would be to identify the sequence of events that led to the accident.
The investigation will consider the actions of those involved, the management of the personnel involved, the agreements established to manage the risk of accidents and any underlying management factor.
Lilli Matson, Health Officer, Security and Environment of TFL, said: “Our thoughts are with the family and friends of the person who sadly died at the Ickenham Metro station last month.
“We are supporting RAIB with his research and we are carrying out our internal research to understand the causes and any action that can avoid such tragic incidents in the future.
“We carry out a wide variety of activities to ensure that our network is safe for everyone at all times, and constantly works to eradicate the risk of such incidents.”
