Nigerian police have opened a murder investigation after the discovery of rotting bodies, skeletons and people shackled with leg-chains in an abandoned building in the southern city of Ibadan.
The discovery on Saturday came after a group of motorcycle taxi riders reported that some of their members had gone missing and were believed to have been kidnapped.
Police also rescued several severely malnourished people found wandering in the bush near the building, investigators said on Sunday.
"When we got to the abandoned building, we saw decomposed corpses, skeletons and skulls in the building and surrounding bushes," Olabisi Ilobanafor, a spokeswoman for Oyo state police, told AFP.
"Seven malnourished human beings looking like living skeletons were also rescued in the bushes surrounding the building. One of them died on the spot while we were there," she said.
Ilobanafor said police had launched a murder investigation and arrested some suspects at the scene in Ibadan, the capital of Oyo state and the third largest city in Nigeria.
"It is not a common occurence in Ibadan or in the state. The police will investigate this crime in all its ramifications," she said.
The grisly find sparked riots outside the abandoned building, dubbed the "House of Horror".
At least 20 people were injured and 12 vehicles damaged when about 50 people brandishing sticks and machetes were prevented from accessing the property on Monday, an AFP correspondent said.
The run-down, one-storey house, surrounded by undergrowth and strewn with the rusted hulks of at least five tractors and a dozen other vehicles, has been cordoned off since the grim discovery Saturday.
Police have so far not divulged any theory on how or why scores of skeletons and rotting corpses came to be found there, but black magic rituals are suspected among locals.
Several severely malnourished people were also found wandering in the bush near the building, which is in the Soka area of the city. Reports said at least 15 others were found shackled inside.
"We want to rescue our people who are still underground and crying for help. But the police are saying no and we are angry," one rioter told AFP.
One man was said by eye-witnesses to have been shot in the stomach by a local gang member in the rioting, one woman added. His condition was not immediately known.