The suspect, Shariful Islam alias Shihab, has been detained from Kushtia early on Sunday, said Dhaka metro police (DMP) spokesperson Deputy Commissioner Maruf Hossain Sardar.
Police said that the suspect belongs to an Islamist militant outfit.
“Shihab is an activist of the Ansarullah Bangla Team. They have been hiding in Khulna since the killing,” Detective Branch Deputy Commissioner Mashrukur Rahman Khaled.
No other details were available, but DMP spokesperson Sardar said that a media briefing will be held later on Sunday over the arrest.
Xulhaz and his theatre activist friend Mahbub Rabbi Tonoy were hacked with meat cleavers on their head and neck, which forensic experts said was to ensure instant death.
Militant outfit ‘Ansar Al Islam’, which claims to be the Bangladesh affiliate of al-Qaeda, had claimed responsibility for the killings as well as six other previous killings of bloggers-online activists and the publisher.
Witnesses said five to seven people, clad in T-shirts and jeans, were involved in the killings and fled the scene after firing from guns, shouting ‘Allahu Akbar’.
The attackers also injured a security guard of the building.
A patrol police officer was also injured while trying to stop them.
He, however, managed to snatch a bag from one of the assailants, inside which two firearms, ammunitions and a mobile phone were found.
Xulhaz’ s family filed a case over the murders the same day against five to six unidentified men while police initiated another over the attack on one of its men and the seizure of firearms.
The Detective Branch is in charge of both of the investigations.