Police today handed over blood samples of the Gulshan café attackers to the US Federal Bureau of Investigation (FBI) for a chemical test in their laboratory.

Masudur Rahman, deputy commissioner of Dhaka Metropolitan Police (DMP) Media wing, confirmed it to The Daily Star.

Doctors on Wednesday collected hair and blood samples from the bodies of six “terrorists” to ascertain whether they had been under the influence of drugs while “carrying out” the attack on a Gulshan café.

A forensic team of Dhaka Medical College Hospital collected the samples on request of Counter Terrorism and Transnational Crime unit of the DMP.

The move came amid media reports that militants, especially members of the Islamic State, are popping addictive pills, which help “fuel their fury”, before attacking the victims.

The six dead include the café's pizza chef Saiful Islam who investigators say was one of the attackers. His family, however, claimed he was innocent.

Blood samples of the family members of the six men were also collected on Wednesday at the lab of the Criminal Investigation Department (CID) in the capital.

On July 1, terrorists stormed the Holey Artisan Bakery in the high security diplomatic zone in Gulshan-2, killing 20 hostages, mostly foreigners. Two police officials were also killed.