Showik Chakraborty (L), Sushant Singh

Widening its probe into the Sushant Singh Rajput death case, the Narcotics Control Bureau (NCB) has detained Showik Chakraborty's school friend Suryadeep Malhotra for questioning, officials said on Monday.

A senior NCB official related to probe told IANS, "We have detained Malhotra for questioning in the drug case."

The official said that he was taken by the NCB from his home in Mumbai after it carried out searches.

This is the 15th arrest in the case so far by the NCB.

Sushant was found dead in his Bandra home flat on June 14 -- triggering a huge political row, an upheaval in Bollywood and simultaneous investigations by the NCB, the Central Bureau of Investigation (CBI) and even the Enforcement Directorate (ED).

The NCB has arrested Sushant's girlfriend Rhea Chakraborty on September 8, her brother Showik, Sushant's house manager Samuel Miranda on September 4, and his personal staff Dipesh Sawant among several others in last few days.

The NCB on Sunday also arrested six more people in connection with the case, including those who supplied drugs to the late actor through his girlfriend Rhea's brother Showik and others.

The six drug peddlers arrested on Sunday were identified as Karanjeet Singh Anand, Dwayne Fernandes, Sanket Patel, Ankush Anreja, Sandeep Gupta and Aftab Fateh Ansari.

An NCB source said that the drug law enforcement agency has also seized the mobile phone of Rhea's mother Sandhya, which was earlier not submitted by her to the financial probe agency.

The source said that the NCB will check the phone if the calls or messages were shared from Sandhya's phone for the procurement of drugs.