Mexican marines may have killed the leader of the brutal Zetas drug cartel in a gun battle in northern Mexico.

The Navy said late on Monday there was “strong evidence” Heriberto Lazcano had been killed in a firefight with marines in the northern state of Coahuila on Sunday afternoon.

If the death of Lazcano, alias “The Executioner,” is confirmed, he would be the most powerful capo to fall in President Felipe Calderon’s military offensive on the gangs.

The Zetas, considered one of the two most powerful drug gangs in Mexico, have perpetrated some of the most sickening acts seen in the country’s drug war that has killed about 60000 people during Calderon’s term. 

Two suspected Zetas gang members who attacked the marines with grenades from a moving car were killed in the gunfight and initial forensic tests suggested one of the bodies was the former soldier Lazcano, the Navy said in a statement.

Lazcano, or “Z-3” is one of Mexico’s most-wanted men and US authorities have offered a reward of up to $5 million for his capture. Only Joaquin “Shorty” Guzman, boss of the Sinaloa Cartel, would represent a bigger prize to the government.

The Zetas were formed by a band of army deserters who acted as enforcers for the Gulf Cartel before breaking away in 2010 to fight a bloody turf war with their former bosses and other drug gangs, including Guzman’s powerful Sinaloa Cartel.

Under Lazcano’s leadership, the Zetas grew from a small group of former soldiers into a gang of more than 10000 gunmen with operations stretching from the Rio Grande, on the border with Texas, to deep into Central America.

Their rapid expansion has displaced Mexico’s older cartels in many areas, giving them a dominant position in the multi-billion-dollar cross-border drug trade, as well as extortion, kidnapping and other criminal businesses.

The Zetas gang had recently appeared to be rupturing due to disputes among leading gang members. A longstanding rivalry between Lazcano and his deputy Miguel Trevino, alias “Z-40,” exploded into violence in recent months.

Since 2009, government troops have caught or killed more than 20 major drug lords. Senior Zetas boss Ivan Velazquez, also known as “El Taliban” or “Z-50,” and Gulf Cartel head Jorge Costilla, alias “El Coss,” were both captured last month.