The Special Investigation Team (SIT) probing the drug racket in Hyderabad has summoned three major courier companies in connection with the case.
Officials of DHL, Blue Dart and Fedex have been asked to appear before SIT, said a statement from the investigation team on Wednesday night.
As the role of postal department has also come under scanner, SIT has written a letter to Chief Post Master General seeking his support in the investigations.
SIT, comprising official from enforcement wing of Prohibition & Excise Department of Telangana, is focusing on how the courier services and also postal department neglected identifying drugs supplied from abroad.
The accused arrested in the sensational case told SIT during the questioning that they received drugs from Netherlands, Germany, USA, Britain and other countries through couriers and post.
SIT will seek an explanation from courier companies on the negligence.
The investigators served notices on the courier companies on a day when they grilled Telugu film director Puri Jagannadh for over 10 hours. They are probing the links of some Tollywood personalities with the drug racket.
SIT has served notices on 12 film personalities including some top actors and actresses for questioning in connection with the case.
The racket was busted earlier this month when the enforcement officials arrested Calvin Mascrenhas and other accused, who revealed that they have been supplying drugs to school and colleges students in the city and some Tollywood artists.
The SIT has so far arrested 13 accused including US citizen, Dundu Anish, an aerospace engineer who had earlier worked with the NASA, and seven B. Tech graduates, most of whom were working for multi-national companies.