During his three-day remand, Rishat agreed to record his confessional statement, said Parimal Das, deputy inspector of Detective Branch of the district police.
Rishat, in his statement, confessed that he participated in the killing and supplied arms for the mission, said Parimal.
Earlier, on Monday, police arrested Nazim and Rishat, two of the suspected hit squad members, who were not named as accused in the case.
On Tuesday, a Cumilla court placed them on a three-day remand each for interrogation and the next day Nazim gave his confessional statement before the magistrate.
Earlier, on 22 November, Sohel, Cumilla City Corporation councillor of ward-17, and one of his aides were killed, while four others sustained injuries when gunmen opened fire in his office in Pathuariapara.
Based on his younger brother Syed Rumon’s complaint, as many as 21 people, some 10 of them unidentified, were booked by the Kotwali police for the double murder.
So far, seven accused and four suspects were arrested in this case, while another accused Rony remains absconding.
Meanwhile, prime accused Shah Alam, Sabbir Hossain, Sajon Mia were killed in alleged gunfights with police.