Investigators are trying to track down relatives of Zetas drug cartel boss Heriberto Lazcano Lazcano, who was killed in a shootout with marines a week ago, to obtain DNA to confirm his identity, the Mexican Attorney General's Office said.

Lazcano's identity was confirmed using fingerprints and photographs of the body, both of which were compared to existing records, the head of the SIEDO organized crime unit of the AG's office, Jose Cuitlahuac Salinas, said.

The body, however, was stolen and officials are trying to prove beyond a doubt that the drug trafficker was killed last Sunday, the SIEDO chief said.

Lazcano, known as "El Lazca," was killed in a shootout with marines in Coahuila state and state prosecutors took charge of the body, which gunmen stole from the morgue.

Investigators took DNA samples from the body before it was taken from the facility.

The Coahuila Attorney General's Office took charge of the bodies of Lazcano and the other man killed in the shootout, and federal authorities were not involved in guarding the remains, Salinas said.

"They were the ones who were responsible for the remains and the evidence in the investigation," the SIEDO chief said.

Investigators face a difficult time finding Lazcano's relatives and getting them to provide DNA to compare to that taken from the drug lord during his autopsy, Salinas said.

President Felipe Calderon and the Navy Secretariat both said they were convinced that the man killed last Sunday was the Zetas cartel's top boss, who was No. 2 on Mexico's list of most-wanted men.

Information provided by the marines corps shows that Lazcano was "killed while resisting the authorities in an operation" in Progreso, a city in northeast Mexico, Calderon said during the inauguration of a prison in Guanajuato last week.

The height of the man killed in the shootout with marines in Coahuila was different from that listed on Lazcano's records, raising doubts in Mexican society about whether the government got the right man.

Lazcano deserted from the Mexican army in 1999 and formed Los Zetas with three other soldiers, all members of an elite special operations unit.

The shootout that killed Lazcano occurred a day after marines captured Zetas regional boss Salvador Alfonso Martinez, who allegedly ordered the killings of more than 300 people, including 72 migrants massacred in 2010 in the northeastern state of Tamaulipas.

After several years as the armed wing of the Gulf cartel, Los Zetas, considered Mexico's most violent criminal organization, went into the drug business on their own account in early 2010 and now control several lucrative territories. EFE