They also believe militants are linked to the mayhem.
“Robbery was not the main objective. Their aim was to kill and unleash violence,” Dhaka Range Deputy Inspector General SM Mahfuzul Haque Nuruzzaman said on Wednesday.
He pointed to the weapons and explosives used in the raid to buttress his claim.
Police arrested two for their alleged links with the heist at the Bangladesh Commerce Bank’s Ashulia branch on Tuesday.
The law enforcers claimed one of those held was involved with the Islami Chhatra Shibir.
State Minister for Home Asaduzzaman Khan also said the militant link to the robbery was being investigated.
Several were injured when eight to 10 robbers hurled bombs while fleeing. They shot and knifed seven dead. A robber was lynched, too.
Almost the entire looted cash of around Tk 700,000 was recovered.
DIG Nuruzzaman told reporters at the Savar Police Station: “I’ve seen many bank robberies, loots. But this incident was different.
“It was not aimed at robbery, but something different.”
“We don’t think it was done for money,” he said.
The manager and two others were killed when the robbers were denied the key.
The robbers fired shots and hurled bombs at the people who gathered outside, killing four others.
The DIG said all the deceased were hacked.
“Nothing like this happened in Bangladesh before. There are many examples of mugging, loot and robbery but there is no instance of such killings,” he said.
Nuruzzaman also said never before had he seen these type of weapons and explosives being used in a robbery.
Referring to RAB’s bomb disposal unit official Maj ‘Khalid’, he said ‘improvised devices’ were made by collecting explosives from foreign countries.
“The bombs they charged are ultramodern. These cannot be bought from outside,” he said.
Two of the robbers were caught but others fled.
RAB had earlier said the bombs were ‘very powerful’.