The National Investigation Agency (NIA) arrested the 10th accused in the killing of Maharashtra's Amravati-based chemist Umesh Kolhe on June 21.
The accused, identified as Shaikh Shakeel, 28, was arrested on Thursday.
The NIA said that Shakeel played an "active role" in the murder conspiracy and resides in the Sarkar Palace area in Amravati.
Earlier, nine accused persons were arrested in the case on June 23, June 24, June 25, July 2, and August 2.
The case was initially registered by Maharashtra Police on June 22 and the NIA re-registered the case on July 2 under various sections of the Indian Penal Code, and sections 16, 18, and 20 of the Unlawful Activities (Prevention) Act, 1967.
NIA FIR says that the killing of Umesh Kolhe was an act of a "larger conspiracy by a group of persons" who conspired to strike terror amongst a section of people of India with their assertions attempted to promote enmity on the grounds of religion.
Mr Kolhe's murder, the FIR also mentions, was carried out as part of the conspiracy to "terrorise a section of the people of India and the case may have national and international linkages".
Mr Kolhe, 54, was killed on June 21 night over a post in support of former Bharatiya Janata Party spokesperson Nupur Sharma on Facebook.
The FIR mentions that City Kotwali Police Station in Maharashtra's Amravati received information about the brutal killing of Mr Kolhe by using a knife and filed a case on June 22 against three unidentified accused persons. The case was registered on the complaint of Sanket Umesh Kolhe, the son of the victim.
The NIA was directed by the Union Home Minister Amit Shah on July 1 to take over the case, and an order followed regarding this from the Ministry of Home Affairs (MHA).
The killing took place exactly a week before tailor Kanhaiyalal Teli was hacked to death in Rajasthan's Udaipur district, a case that shocked the whole country.