At least 20 people have been murdered and others wounded at a Sufi shrine near the city of Sargodha, in Pakistan's Punjab province, police say.
Deputy police commissioner Liaquat Ali Chatta said the main suspect was the shrine's custodian, Abdul Waheed.
The shrine was run by a Sufi saint, Muhammad Ali Gujjar, who was not there on the day of the murders.
One survivor told police Mr Waheed had called followers into his chamber one by one, and gave them poisoned food.
He and his companions then killed them with a dagger and a stick.
The alarm was raised by an injured woman at a nearby hospital who had managed to escape.
Local police then rushed to the shrine and arrested Mr Waheed, along with several others believed to be his accomplices.
The motive is unclear, but one senior local police officer said the suspect appeared to be mentally unstable, or that the killings could be related to rivalry for control of the shrine.
"The 50-year-old shrine custodian Abdul Waheed has confessed that he killed these people because he feared that they had come to kill him," Zulfiqar Hameed told AFP.
Pakistan's Geo TV said the victims were tortured before they were killed, and that their bodies were found unclothed.
Three survivors managed to flee the scene of the crime. According to one, they attacked the suspects after some children witnessed the incident through a door.
Reports suggest the victims may have been pilgrims. Police said it was customary for food to be distributed at the shrine during the first week of Rajab, a scared month of the Islamic calendar which began at the end of March.
Source: BBC News