The attackers moved from house to house with a list of suspected witches
Nineteen people have been arrested in Kenya in connection with the burning of 11 people accused of being witches.
A police spokesman told the BBC that those arrested may not have been involved in the killings but possibly incited the attacks.
Eight women and three men, aged between 80 and 96, were burned to death in the western Kisii district on Wednesday.
A security operation was launched to hunt down the villagers involved. The area is now reported to be calm.
The Kisii district has witnessed similar attacks in the past when people suspected of engaging in witchcraft have been killed or ostracised.
But our reporter says that this is a surprisingly large number of people to be attacked at the same time.
Deputy police spokesman Charles Owino told the BBC:
"You may find that they could not have been involved directly in the killing, but if you have evidence that they were involved in war cries, then they will have another offence of inciting," he said.
He said those proven to have been involved in the attack would be charged with murder.
The police are guarding against revenge attacks, the police spokesman said.
The BBC's Muliro Telewa in the region says the gang had a list of the victims and picked them out individually.
The mob dragged them out of their houses and burned them individually and then set their homes alight, our correspondent says.
Police at the murder scene
Residents have been ambivalent about condemning the attacks because belief in witchcraft is widespread in the area, he says.
But local official Mwangi Ngunyi spoke out against the murders.
"People must not take the law into their own hands simply because they suspect someone," he told AFP news agency.
Villagers told reporters that they had evidence that the victims were witches.
They say they found an exercise book at a local primary school that contained the minutes of a "witches' meeting" which detailed who was going to be bewitched next.
The victim's families are in hiding, fearing for their lives.
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