The attackers seized the Holey Artisan Bakery on the night of July 1, where they murdered 20 hostages.
Bangladeshi investigators have sought more samples from the bodies of the slain attackers to check whether the ISIS' 'super soldiers' carried out the country's worst terror attack at an upscale restaurant in Dhaka's diplomatic zone early this month, killing 22 people.
"Police's counter-terrorism unit has asked for samples of hair, 20 mililitres of blood among other things. So we will 'extract them from the dead bodies," assistant professor of Forensic Medicine at Dhaka Medical College and Hospital Soheil Mahmud was quoted as saying by the bdnews24.com on Wednesday.
The autopsy officials took samples of the attackers' blood, teeth and flesh from their thighs to check if they were under the influence of drugs the ISIS uses to create "super soldiers", said Mahmud.
"We had collected five mililitres of their blood. But the investigators want 20 mililitres and more samples. We will collect them at a suitable time," he said.
ISIS fighters use an amphetamine-based drug in the form of a pill, Captagon, for energy and agility at the battlefront, according to investigators and military analysts.
According to experts, Captagon users can go on without sleeping for days and without feeling hungry.
The attackers, mostly in their 20s, seized the Holey Artisan Bakery on the night of July 1, where they murdered 20 hostages, 17 of them foreigners. Two police officers died when hit by a grenade. The six gunmen were killed by army commandos who stormed the cafe the next morning.
The remains of the attackers are kept at the mortuary of the Combined Military Hospital in Dhaka.
The so-called ISIS claimed responsibility for the deadly attack, but the government denied their presence in Bangladesh, saying homegrown terrorists were responsible.
The elite anti-crime Rapid Action Battalion yesterday released a CCTV footage of four suspected terrorists including a woman linked to the cafe attack.
In the video, the four are seen strolling around the cafe ahead of the attack and talking among themselves while the young woman was carrying something heavy in a vanity bag.
However, none of their faces appear clear in the footage.