The Police Bureau of Investigation (PBI) has detained Chattogram's former police superintendent Babul Akter after allegedly establishing his involvement in his wife's murder. PBI officials, however, told UNB on Wednesday that they would formally place Babul under arrest only after getting a fresh complaint from the father of his deceased wife. Based on the complaint, officials said, the PBI will lodge a fresh FIR for murder. Banoj Kumar Majumdar, Deputy Inspector General of PBI, said, “Mahmuda Khanam Mitu's father Mosharraf Hossain will file a fresh complaint in the case, following which Babul will be formally arrested in the case.” “As of now, Babul has not been arrested as he is the complainant in the murder case. We have already prepared the final report in the case and will soon submit it in the court,” he said. Sources told UNB that Babul was detained by PBI sleuths on Tuesday night, after hours of questioning. Santosh Kumar Chakma, investigating officer, said that Babul himself came to the PBI office in Mansurabad on Tuesday afternoon to check the progress of the murder case. On June 5, 2016, unidentified assailants gunned down Babul's wife Mahmuda Khanam Mitu at the port city's GEC intersection while she was going to drop her son Mahir Akhter, 7, for a bus of Chittagong Cantonment Public School and College. Read: Ex-SP Babul Akter finally held over 2016 murder of wife Mitu Soon after the crime, Babul had filed a murder case at Panchlaish Police Station against three unidentified men. Later, Chattogram Metropolitan Police arrested four men, including Abu Nasur Gunu, Shah Zaman alias Robin, Md Anwar and Md Motaleb Mia alias Wasim, from different places in connection with the murder. Of them, Anwar and Wasim gave confessional statements before a magistrate, implicating seven people, including Musa who directly took part in the killing, Mohammad Rashed and Nabi. During the course of the probe, police had also arrested "arms supplier" Ehteshamul Haque Bhola and his assistant Md Monir and seized a pistol from their possession. Cops had also nabbed Musa's elder brother Saidul Shikder Shakur and Shahjahan for providing the motorbike that was used in the murder. But on July 4, 2016, Nabi and Rashed were killed in a gunfight with police in Rangunia. The case was transferred to the PBI in 2019, after Mitu's father, himself a retired police officer, filed a complaint against the CMP's mishandling of the case. Mitu's father had, in fact, accused Babul of being directly involved in the murder case. "He (Babul) should be implicated in the murder case... if he's not, we'll go to the court." Babul was called for questioning a number of times by the PBI since his transfer, but had never been detained.