Mexican police seek DNA of missing to identify decapitated bodies May 16, 2012 -- Updated 2044 GMT (0444 HKT) DNA samples will be the only way to identify the decapitated victims, a state official says Authorities are seeking DNA from families of missing persons Investigators are trying to identify the 49 bodies, and who was behind the deaths Banners claim the Zetas drug cartel was not responsible for the gruesome crime Monterrey, Mexico (CNN) -- Mexican authorities are asking for DNA samples from families of missing persons nationwide in their efforts to identify 49 decapitated bodies, an official said Wednesday. That will be the only way to identify the victims -- whose killers cut off their heads, hands and feet -- Nuevo Leon state security spokesman Jorge Domene told reporters three days after investigators found the remains abandoned along a highway. Officials in El Salvador may also request access to the DNA data authorities in Nuevo Leon have compiled, to compare it with samples from family members of Salvadoran migrants who have gone missing in Mexico, Domene said. While investigators work to identify the victims behind closed doors, parts of the case have played out quite publicly. Banners hanging in locations throughout the country, purportedly from the Zetas, claim that the notoriously ruthless cartel had nothing to do with the gruesome crime. But another message purportedly signed by the Zetas and found Sunday at the crime scene -- a roadside near the industrial city of Monterrey and about 80 miles southwest of the U.S. border -- told a different story, threatening members of rival cartels and Mexican authorities. Domene told reporters Wednesday that investigations to find those responsible would focus on scientific proof and not on the banners. On Monday, Mexico's interior minister said the 49 decapitated bodies were likely the result of a fierce feud over territory and power between the Zetas and members of the allied Gulf and Sinaloa cartels. Interior Minister Alejandro Poire stressed Monday that the Mexican government would not retreat from its efforts to crack down on organized crime -- an effort that is facing increasing criticism as Mexico's presidential campaign season heats up. More than 47,500 people have died in drug-related violence in Mexico since December 2006, when Calderon announced plans to deploy troops in efforts to combat cartels.