The Gulshan café attackers' photos reportedly released by Islamic State were taken at a flat in the capital's Bashundhara residential area days before the July 1 attack, police said.
The flat, which is in a Block-E building on Road-6, belongs to Prof Gias Uddin Ahsan of North South University, according to police.
Prof Gias was arrested on July 16 on charges of renting out the flat to the café attackers and withholding tenants' information from law enforcers. Police also arrested his nephew Alam Chowdhury and manager of the building Mahbubur Rahman Tuhin on the same charges.
The US-based Site Intelligence, which monitors jihadi activities, posted separate photos of the five youths around 10:00pm on July 2, saying the images were released by the global terror body.
In the post, the five were mentioned as “Dhaka attackers”. All in black panjabi and keffiyeh, they were grinning, holding AK-22 guns. A black cloth resembling the Islamic State flag was used as the background in each of the photos.
According to SITE, Islamic State claimed credit for the attack, which left 22 people, including two police officials and 17 foreigners, killed at Holey Artisan Bakery in Gulshan's diplomatic zone.
“Our investigation found the militants had the photographs taken at their flat in Bashundhara residential area,” Monirul Islam, additional commissioner and chief of counterterrorism unit of Dhaka Metropolitan Police, told The Daily Star on Sunday.
Investigators believe the “black flag” seen in the photographs of the Gulshan attackers was the one they recovered during the operation “Storm 26” at another militant den, a flat in a Kalyanpur building.
Police claimed to have recovered several similar pictures of nine militants killed at the Kalyanpur den on July 26.
Earlier, Monirul said a faction of Jama'atul Mujahideen Bangladesh (JMB) known as “New JMB” attacked the upscale Gulshan eatery.
Tamim Ahmed Chowdhury, a Bangladesh-born Canadian citizen, who has been staying in the country since 2013, is the coordinator of “New JMB” and one of the masterminds of the Gulshan attack, he added.
Investigators think the militants took the photographs several days before the café siege and sent those to Tamim.
Tamim or his accomplices might have sent the photographs to Amaq news agency of Islamic State after the five militants stormed the Gulshan eatery and held diners hostage at gunpoint, said a police official, preferring anonymity.
To launch the attack, the gunmen went to the café from their Bashundhara flat, he added.
A carton loaded with sand and dresses left behind by the militants were also seized from the flat, police say, as they suspect the carton was used for keeping grenades.