Suspect shot in the leg while fleeing scene of the crime in the Schaerbeek neighborhood of Brussels.
Youssef Kobo, the adviser on diversity for the minister in charge of equal opportunity in the regional government of Brussels, said he was 'young and stupid' when he wrote the Facebook posts in 2014, which he later claimed to regret.
The clip of the young man, the son of a radical cleric, was disseminated by a Middle East monitoring group.
Assailant dies of wounds after being shot by police, local media reports.
As of yet, there is no connection with the attacks at Brussels airport and the metro on March 22, in which 32 people were killed, the prosecution office says.
The man, identified only as J.B., says he was abducted and fitted with an explosive device, which was later found to be laden with salt and cookies.
The authorities say the teens did not apply quickly enough after their parents died in the May 2014 attack in Brussels.
Belgian authorities have transferred EU's most wanted fugitive; Abdeslam is only surviving perpetrator of November's deadly attack in the French capital.
Police are looking for the assailant behind the box cutter attack and whose motives are yet unclear.
Salah Abdeslam, who is due to be extradited to France, was charged over a police shootout in Brussels that wounded four police officers.