The Mexican army says it has arrested the man believed to have ordered the killing of 49 people.
Their mutilated bodies were found dumped by a roadside near the city of Monterrey in the northern Nuevo Leon state a week ago.
The 43 men and six women had been decapitated and their hands were cut off.
An army spokesman said Daniel Jesus Elizondo - known as El Loco, (The Madman) - was arrested by troops.
He is reported to the leader of the Zetas drug cartel in the region.