Due to poor management and inefficiency of police officials, the bomb went off inside the Pallabi Police Station compound and left five people, including four police personnel, injured on July 29, investigators said.
They said the officials were not supposed to take the bomb inside the compound after recovery, failed to handle it properly, did not inform the bomb disposal unit on time, and supervising officers including the officer-in-charge and the deputy commissioner of Mirpur division failed to give proper instructions.
Investigators came up with such findings a week after the probe began.
On July 30, a day after the blast, Dhaka Metropolitan Police (DMP) formed a three-member probe body with its Joint Commissioner (operations) Monir Hossain as the chief.
The team was asked to gather details of the blast, determine the nature of the bomb and find its source.
It was also asked to collect details about the handling of the bomb inside the police station compound, and assess the responsibility of the officer concerned and his team.
Joint Commissioner (operation) Monir told The Business Standard the probe committee had submitted the report to the DMP commissioner on Monday.
DMP Commissioner Shafiqul Islam said he had received the report but had not gone through the details yet.
"The bomb was not handled properly inside the police station compound and the police officials acted non-professionally," he replied when asked about the findings of the probe committee.
On August 8, the DMP authorities transferred Mirpur division Deputy Commissioner Mostaq Ahmed, Additional Deputy Commissioner (Pallabi zone) Mizanur Rahman, Assistant Commissioner (Pallabi zone) Firoz Kawsar, Pallabi Police Station Officer-in-Charge Nazrul Islam, Inspector (investigation) Abdul Mabud, and Inspector (operation) Emranul Islam.
When asked about the transfers, the DMP commissioner said those were part of regular postings and were not the result of any punishment.
"I need to go through the probe report and separate punitive measures will be taken against whoever is found responsible," he added.
Negligence of Mirpur division
Probe officials said their investigation had revealed the names of two underworld criminals – Jamil and Mamun.
The two are brothers and are believed to be hiding somewhere in India and Nepal, they said.
"The brothers accepted the contract to kill Pallabi Police Station Jubo League unit's General Secretary Juwel Rana and Taizul Islam Bappi, councillor of ward 6. Their plan was to kill either Juwel or Bappi as part of the deal," said a police official involved in the investigation.
Based on a tip-off, police arrested Shahidul Islam, Mosharraf Hossain and Rafiqul Islam from different areas on July 28 and 29.
They are Jamil's associates, sources said.
"Here comes a twist. After the arrest of the three men, councillor Bappi made a deal with a section of Mirpur division police and promised to provide them with around Tk2 crore. As per the plan, police were supposed to show the three arrestees as supporters of Juwel," said the official.
Both Bappi and Juwel have a close relation with ruling party lawmaker Elias Mollah.
"But Bappi wanted to get rid of Juwel as the latter is also trying to contest as a councillor. Besides, Bappi wanted to establish supremacy and control in Pallabi area, something Juwel is doing now. For this reason, Bappi wanted to include Juwel's name in criminal activities," according to investigation sources.
As per the plan, police took the three arrestees near Kalshi graveyard area and collected a firearm from Bappi. Police also collected bombs and bullets from his associates, sources claimed.
When police were trying to assemble those inside the police station compound, one of the bombs went off, said officials involved in the investigation.
The blast foiled the arrest plot and the Islamic State later claimed responsibility.
A high official of the DMP, requesting anonymity, said the top six officials of Mirpur division were transferred after investigators had learned about the plot.
The Special Action Group (SAG) of the Counter Terrorism and Transnational Crime (CTTC) unit is now investigating the case filed over the blast.
Abdul Mannan, deputy commissioner of SAG, said the probe had revealed some information and they had found the involvement of a number of people in the incident.
But he refused to disclose further details for the sake of investigation, saying, "We are now analysing the facts."
Bappi told The Business Standard he has very good relations with Juwel and they are doing politics together.
"We both have good relations with the local parliamentarian," he said.
He also said he was not involved in any plot.
"May be some people are spreading rumours against me to tarnish my political image and destroy my relationship with Juwel," said Bappi.
He said he had come to know that someone wanted to kill both him and Juwel, but did not disclose the name.
"I do not want to mention any name. Police are investigating the case and we are expecting a fair probe."
Juwel could not be reached for comment.
A high official of the DMP involved in the investigation said probe had stalled as Jamil is out of the country.
"We are now trying to detect his associates' hideout and collect information about their activities. Once they are arrested, we will able to give further information about the incident," he said, requesting anonymity.