"Hair and blood samples from the five gunmen and their suspected aide have been given to the Federal Bureau of Investigation for testing," said Deputy Commissioner Masudur Rahman.
Immediately after the attack on July 1, US Secretary of State John Kerry called Bangladesh Prime Minister Sheikh Hasina and offered her assistance from American law enforcement agencies, including FBI.
The counter-terror unit asked for hair and 20 mililitres of blood to be collected from the bodies for a second time, Soheil Mahmud, assistant professor of Forensics Medicine at Dhaka Medical College and Hospital said.
The autopsy will check if they were under the influence of amphetamine-based drugs, namely Captagon, that the IS uses to create 'super soldiers', Mahmud said.
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A forensic team of Dhaka Medical College Hospital collected the samples on request of Counter Terrorism and Transnational Crime unit of the Dhaka Metropolitan Police.
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.
Two police officers also died during the attack, for which the Islamic State claimed responsibility.
The government said six attackers were killed by army commandos, who stormed the cafe the next morning.
Among them, five were members of the banned Jama'aatul Mujahideen Bangladesh (JMB), according to the police. They maintained that the sixth person, the restaurant's chef, Saiful Chowkider, "was assisting the killers".
The remains of the attackers and their alleged aide were at the mortuary of the Combined Military Hospital (CMH) in Dhaka.