DHAKA (Reuters) - Police in Dhaka on Saturday arrested three people and another on Sunday, including a university professor, for failing to register information about tenants renting property who later attacked a cafe in the city, killing 20 people.

People attend a candle light vigil for the victims of the attack on the Holey Artisan Bakery and the O'Kitchen Restaurant, in Dhaka, Bangladesh, July 3, 2016. REUTERS/Adnan Abidi

Gias Uddin Ahsan, a professor at North South University in Dhaka, his nephew, and the manager of Ahsan’s apartment were arrested by Dhaka Metropolitan Police (DMP) for failing to comply with rules forcing landlords to register information about their tenants with the police, Mohammad Masudur Rahman, a senior police official told Reuters.

He said police also arrested a landlord on Sunday for not disclosing information about his tenants who were also suspected of being associated with the attack earlier this month.

Mohammad Nurul Islam, owner of another house in the city did not register information about his tenants and police found grenades and black clothing in the house, similar to the clothing worn by the attackers, police said.

After appearing in court on Sunday, they were remanded by police for eight days, he said.

They had rented the house for 22,000 taka ($275) per month, paying two months in advance.

“They used to meet there from time to time to make plans and they were 7 to 8 members, after the attack they fled away,” he said.

Five militants who were killed by police after they stormed the cafe on July 1 had rented the apartment along with another person in a nearby residential area in May and started living there from June, Rahman said.

“From here they attacked the cafe. There were other militants also who fled after the attack,” he said.

“We also found evidence that they kept grenades and other explosives in the apartment. If we had been informed they were living there, then that brutal killing would not have been possible and we could also have arrested the other militants who fled.”

Earlier this year, the DMP issued an order to all apartment owners to provide details of their tenants for a database to help police crack down on criminals and militants using rented accommodation as hideouts.

A spokesman for the university told Reuters the university was surprised. “The authority will provide all cooperation to the law enforcing agency in this investigation,” he said.

Bangladesh has suffered a series of attacks on liberal bloggers, university teachers and members of religious minorities over the past year. The government says two domestic militant groups trying to replace secular democracy with Islamic sharing rule are responsible for the violence.

Twenty people including 18 foreigners were killed before police stormed the cafe, rescued 13 hostages and shot five of the attackers dead.

Interior Minister Asaduzzaman Khan said on Saturday that investigators had identified the masterminds of the attack and that the remaining perpetrators would soon be arrested.

Some of the assailants had attended prestigious schools or universities and had been reported missing, according to the police. One was the son of a politician.