Nilima Araj, police inspector, City Kotwali Police Station, Amravati, said that the detainees are being questioned, news agency ANI reported.
The police have further appealed to people to contact the nearest police station if someone threatens them directly or indirectly over their post on Nupur Sharma, said Amravati Police Commissioner Arti Singh.
She added that the details of the complainant will be kept confidential.
On 17 June, after some people reached his residence to threaten him, he left Nagpur with his family.
The Amravati murder took place on 21 June around 10 pm, when Kolhe had closed his shop, Amit Medical Store, located in Rachana Shree Mall near the Amravati Tehsil office.
Umesh Kolhe was one among the 14 people threatened over their social media posts in Amravati and was murdered on his way home.
The National Investigation Agency (NIA) took over the custody of seven accused in the murder on Tuesday, 5 July.
While the seven have been sent to a four-day-transit-remand, they will be presented before a Mumbai court on 8 July. The eighth accused in the case is on the run.
Meanwhile, Kanhaiya Lal was killed by Riaz Akhtari and Gos Mohammad on 28 June for supporting Sharma. The two men filmed the killing and later posted a video bragging about it. They were arrested just hours after the incident took place.