New Delhi - Bangladesh police said on Monday they have formally arrested a detained attacker and one other over a siege at a café in which 20 hostages were killed."Two people are in custody. We'll file a case," inspector general of police Shahidul Hoque told AFP.Security officials on Monday questioned some of the people rescued and pursued information on the possible masterminds.An official involved in the investigation said authorities were still holding five of the 13 people rescued when commandos stormed the restaurant in Dhaka's diplomatic zone Saturday morning, killing six of the attackers and capturing one.Those being held include a Canadian citizen of Bangladeshi origin, as well as a Bangladesh-born British citizen, the official said on condition of anonymity, as he was not authorised to speak to media about the ongoing investigation.He confirmed investigators were also speaking with a third man described by local media as a Bangladeshi who was trapped inside the restaurant along with his wife and two children. The man, a teacher at a private university in Dhaka, had returned to Bangladesh recently after living in Britain for nearly 20 years.Several crude videos taken from an apartment near the Holey Artisan Bakery show the man talking to the attackers, who allowed him to leave before paramilitary forces launched the rescue operation on Saturday. The man's friends and police also said the one of the attackers was a student in the same department at the university where the man teaches.The official would give no other details of the identities of the five rescued people being questioned, but said authorities were looking into their backgrounds and questioning their family and friends as well.The brutality of the attack - the worst convulsion of violence yet in the recent series of deadly attacks to hit Bangladesh - has stunned the traditionally moderate Muslim nation and raised global concerns about whether it can cope with the increasingly strident Islamist militants.That the attackers targeted a popular restaurant in the heart of the diplomatic quarter of Bangladesh's capital signaled a shift in militant tactics. Previously, most attacks were carried out by gangs of young men wielding cleavers and machetes and hacking into their victims before fleeing.‘The nation is shattered’The English-language Daily Star newspaper on Monday said the bloody hostage crisis had left "the nation shattered and with a sense of extreme unease". The editorial also criticised authorities' consistent denial of the presence of any international terrorist groups, even as the Islamic State group claimed responsibility for the attack and released gruesome photographs that apparently depicted the torture of hostages."The methods employed and the savagery with which the killings were carried out are hallmarks of international terrorist outfits like Isis and Al-Qaeda. This is clear," the paper says in its editorial. "What is not clear is whether, after such overwhelming evidence of their presence, the official line will be one of denial?"Bangladesh police have said they are investigating whether the attackers had links with the extremist Sunni Muslim group based in Syria and Iraq. But the home minister insisted IS could not have guided the attack from abroad, as he said it has no presence in Bangladesh.Instead, Prime Minister Sheikh Hasina's government said the attacks are being carried out by domestic militants bent on imposing Islamic rule, and blames the political opposition of backing the attacks in order to create chaos in the country.On Monday, surrounded by tearful family members and a heavy security detail, Hasina and diplomats from Italy, Japan and other countries lay flower wreaths beside the coffins holding the three Bangladeshi victims.Another 17 hostages, nine Italians, seven Japanese and one Indian, were killed in the attack - many of them tortured with sharp instruments, according to police.Those bodies were to be flown back to their home countries later on Monday. Two additional deaths were of police officers killed on Friday night when police engaged the attackers in a gun battle at the start of the crisis.The stadium vigil was visited by hundreds of Dhaka residents, paying their respects to the victims.A Catholic Mass, Islamic prayer sessions and a candlelight vigil were being held throughout Monday.