The two American missionaries strangled to death in the northern Mexican town of Santiago knew their killer, the Nuevo León state attorney general said Thursday.
"We didn't find that the doors were forced to enter the property," Adrian de la Garza told a press conference here. "It's probable that the killer knew them, by virtue that the one who did this was inside the house by the will of the people who lived in it."
The bodies of Wanda Casias, 67, and John Frank Casias, 76, who came to Mexico from Colorado three decades ago, were found Tuesday by their son at a ranch about 37 kilometers (23 miles) from Monterrey, the state capital.
The woman's body was found in the kitchen and the man's body was in the yard. Both victims were beaten and then strangled with wire, which was found around their necks.
The couple were missionaries with the First Independent Fundamentalist Baptist Church.
"We have some lines of investigation that are already being followed and we will pursue it to the final consequences," De la Garza said Thursday.
Neighbors told detectives the couple was active in aiding the community and that it was not unusual for them to invite people into their home.
Electric appliances, a pick-up truck and other property were missing from the house.
"All the possibilities are being investigated, including that of organized crime," the state attorney general said.
Santiago, a popular tourist destination, has been rocked by drug-related violence in recent years.
Mayor Edelmiro Cavazos was kidnapped and murdered on Aug. 15, 2010, by gunmen working for the Los Zetas drug cartel, which was trying to take control of the town.
Santiago police officers assisted the hired guns who killed the mayor.
The mayor was the victim of what Mexican officials call a "levanton," a kidnapping with no ransom demands usually staged by drug cartel enforcers to obtain information via torture or to kill the victim for having betrayed the criminal organization.