Three Roman Catholic priests have been murdered and another tortured in Mexico since September, reports the Associated Press.

Rev. Jose Luis Sanchez Ruiz was found alive three days after his abduction in Catemaco town, Veracruz state, with ‘visible signs of torture’ according to a Roman Catholic Church statement. His kidnap came after the abduction and fatal shooting of two other priests in the same state in September. This followed the murder of another priest in Michoacan state in the same month. A suspect has been arrested in the case of the double murder.

While prosecutors have suggested that robbery may have been the motive in all three killings this year, Sanchez Ruiz “had received threats in recent days because he is a defender of human rights and social causes. He has criticized the system of corruption and the crime problem in Catemaco,” according to Rev. Aaron Reyes, a spokesman for the diocese, in an interview with Milenio television news.

At least 31 priests have been killed in Mexico since 2006, with the majority of attacks taking place in areas of Mexico plagued by drug cartel violence, including Veracruz, Michoacan, Guerrero and Mexico states.