Nuevo Leon state security spokesman Jorge Domene says the Zetas deserters told investigators that they left the Zetas and joined the Gulf cartel because they hadn't been paid in months.
Domene said Friday that the seven had jumped to the Gulf cartel in recent months and were working as assassins. He says the 24 detainees, including two teenage girls, confessed to participating in at least 48 homicides.
The Zetas first worked for the Gulf cartel, which dominated drug trafficking along Mexico's northeastern border with Texas. But the two groups split in 2010, leading to an unprecedented escalation in drug violence in that region.