Authorities in Mexico said Thursday that they found a total of 166 skulls in clandestine burial pits that are frequently used by drug cartels to dispose of their victims.

Along with the skulls, found in the Gulf Coast state of Veracruz, investigators discovered 114 identification cards as well as other personal possessions. The field held about 32 burial pits, according to Veracruz state prosecutor Jorge Winckler.

Winckler did not reveal the exact location of the site, citing security reasons. But authorities said it was one of the biggest mass grave sites discovered so far in Mexico.

Investigators began searching for the pits about a month ago using drones, probes and ground-penetrating radar after a witness tipped off prosecutors that “hundreds of bodies” were buried there.

Veracruz is known for heavy violence between the Zetas and Jalisco drug cartels, in addition to kidnappings and extortions that plagued the state.

Families in search of missing loved ones were invited to the state capital of Xalapa, where they will be shown photos of items found at the site to help identify the remains.

Maria de Lourdes Rosales Calvo, whose son was abducted with his girlfriend in July 2013, said the news of the gravesite “gives hope.” She said her son was 25 years old when he was abducted by four armed men just blocks away from her home, and that authorities brushed it off by saying the couple had run off together.

Veracruz investigators have found several mass gravesites in recent years, finding 253 skulls and bodies in burial pits outside the state capital in 2016 and 2017, after receiving a hand-drawn map of the locations of the graves from relatives of missing people.

In the capital of northern Durango state, which is also named Durango, police found 236 bodies in burial pits in 2011.

Just north of Vereacruz, in the town of San Fernando in Tamaulipas state, authorities found 193 bodies that were mostly Mexican migrants kidnapped while on their way to the United States and killed by the Zetas cartel.

The Associated Press contributed to this report.