"The CCTV footage is of poor quality and does not have visuals of the person who dropped off the letter (allegedly from Indian Mujahideen). We have other leads and these are being pursued," said a crime branch officer.
They have also started questioning the staff, although no clues have been got.
A threat letter was sent to Ambani on Feb 24 after which police tightened his security. Although the letter said it was from the Indian Mujahideen, who claim they will carry out a terror attack on his house in South Mumbai the police are unsure of it's authenticity.
The letter addressed to Ambani stated that they would harm him or his residence for his support to Gujarat chief minister Narendra Modi. According to reports, the letter stated that Ambani had 'hurt the minority community's sentiments by supporting Narendra Modi and blamed him for grabbing Waqf board property, where his residence is built'. It also said that the 'IM is upset over Ambani's heavy investment in Gujarat'. The letter also reportedly demands the release of arrested Indian Mujahideen operative Danish.