Investigators are examining a video recovered from the mobile phone of martial arts instructor Shah Amanat Sabir.

Sabir, 23, chief instructor of Fatah Combat System, and his aide Hossain Tanim, 20, were placed on a fresh three-day remand by Dhaka Metropolitan Magistrate Ariful Islam after the investigators placed a seven-day remand prayer. Four others arrested with them on July 5 from Jatrabari’s “Mini Cox’s Bazar” area were sent to jail following a police application.

During the hearing, the judge noted that police had not shown the accused arrested under the Anti-Terrorism Act at this stage, saying remand was granted “solely for the sake of a fair investigation.” He assured that if nothing was found during interrogation, the accused would be released.

The court directed investigators to submit a report by July 12.

Among the arrestees is Ataullah Shah, joint member secretary of the National Citizen Party’s Gazipur city convening committee, who was expelled by the party on July 7 following his arrest. In a notification, NCP said Ataullah was permanently removed from all posts and membership for "activities contrary to party principles."

Investigators said they are examining whether the video found on Shah Amanat Sabir's phone, martial arts training, and organisational links point to the formation of a small extremist group.

The two-minute-23-second clip shows explosions on a rural road at night, militant-style slogans, and Sabir issuing threats while holding a sharp weapon. An Arabic song linked to Islamic State propaganda was used in the background, officials said.

Officials, however, did not disclose where and when the video was recorded or to whom it was later sent.

During interrogation, Sabir claimed that the video was recorded by his associates and that they had added the song before sending it to someone abroad, investigators said.

A police official told The Daily Star that Sabir had formed “SBJ” [short for "Sabir Bhaiyer Jama"], with 13 to 15 members, adopting the title “Ameer-e-mujahid.”

The official, requesting anonymity, said “jama” was used as a shortened form of “jamaat”, meaning a group or collective. He mentioned that the group was not formally linked to any known organisation.

The official added that Sabir had approached leaders of banned outfits Ansar Al Islam and Harkat-ul-Jihad-al-Islami Bangladesh but later formed his own group after disagreements over ideology and strategy.