The railway police has sought permission from the court to perform brain mapping, polygraph and narco analysis test on Railway Protection Force constable Chetan Singh who is accused of shooting dead four persons, including his senior colleague, on board a Jaipur-Mumbai train on July 31.

Seeking permission for brain mapping, polygraph and narco analysis test, the Government Railway Police (GRP) told the magistrate court in Borivali that the matter was very serious and a thorough investigation was needed.