Biswanath Chariali police district SP Manabendra Dev Ray said seven persons were arrested on Monday and another nine today from Vimajuli village where the incident took place yesterday.
Villagers of Vimajuli, however, protested against the police action and justified the killing saying she was practising witchcraft on them.
The body of the woman was today sent to her village for cremation after post mortem at Biswanath Chariali Civil Hospital, police said.
Meanwhile, Assam Tea Tribe Student Association (ATTSA) district president Krishna Kamal Tanti said, "We vehemently condemn the barbaric incident and demand booking of all culprits to give them exemplary punishment."
Vimajuli is about 110 km from Tezpur and is a remote area bordering Arunachal Pradesh in Sonitpur district with most of the people being Adivasis and Karbi tribes. They did not have proper education and health facilities.