The Delhi Police's Crime Branch on Wednesday arrested the brother-in-law of the owner of the Anaj Mandi building, where a massive blaze claimed 43 lives, police said.
The building's owner Rehan and his manager Furkan were arrested on Sunday after the incident.
Police had said, during their interrogation, it was learnt that a portion of the building was owned by Rehan's brother-in-law Suhail.
Suhail was arrested on Wednesday, police said.