Kawsar Hossain Khan and Kamal Hossain were presented before Dhaka's Chief Metropolitan Magistrate's Court yesterday after their five-day remand ended. The two were arrested on August 27.
The case's investigating officer, Detective Branch Inspector Mahmudur Rahman, had sought custody of the duo for another seven days.
But Magistrate Lutfor Rahman Shishir granted four days to question them, bdnews24 reported.
Neel was killed by five assailants on August 7 inside his fifth-floor flat in the capital where he lived with his family. The assailants entered the flat after Friday prayers, pushed his wife and one of his friends aside and then hacked him to death.
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He was an official of NGO Ganajagaran Mancha which waged a massive campaign for the capital punishment for war criminals who carried out atrocities siding with the Pakistani troops in 1971.
Apart from Neel, other bloggers killed in Bangladesh this year are Ananta Bijoy Das, Washiqur Rahman and Avijit Roy.
The murders of secular bloggers sparked international outrage with the UN, the US and Britain expressing concern against shrinking space for free thought.