The terror siege at Holey Artisan Bakery in the Gulshan diplomatic enclave on Jul 1 last year killed 20 people including 17 foreigners.
"There were not only Bangladeshi victims. Nationals from friendly countries like Japan, Italy, India and the USA were also killed in the attack. So, we are trying to make it flawless," he told reporters at his Secretariat office on Wednesday.
The army commandos were called in to end the overnight seige and carnage by young Islamist militants. Five militants and a restaurant worker were killed in the brief but lethal operation.
Four others are now in police custody and the hunt for a number of other accomplices is on, according to the investigators.
The home minister termed the Holey Artisan attack a 'turning point' in combating terrorism in Bangladesh.
"We are minutely looking into each and every issue relating to the incident. So, it's taking some time to finalise the charge sheet," he added.