Updated

Federal agents have captured two of 53 inmates who escaped from a prison in northern Mexico last month as its guards apparently stood by, federal police said Thursday.

Marcos Espinoza and Osvaldo Garcia were detained Wednesday in Mexico's central state of Hidalgo along with six alleged members of the Zetas, a gang of hit men tied to the Gulf cartel, federal police intelligence coordinator Luis Cardenas told reporters.

Security camera footage shows that guards at the Cieneguillas prison in Zacatecas state stood by as an armed gang walked out with the 53 inmates on May 16. About a dozen of the fugitives are drug cartel suspects.

The prison director and all 44 guards on duty have been jailed pending an investigation into their possible complicity.

Mexican drug gangs often buy off or blackmail guards and police. President Felipe Calderon's government has stepped up its campaign to fight that kind of corruption in recent weeks, arresting dozens of police and elected officials — including 10 mayors in his home state of Michoacan — on suspicion of collaborating with drug traffickers.

Soldiers raided police stations in the northern state of Nuevo Leon for a fourth day on Thursday, detaining two police chiefs for questioning. More than 70 officers from 13 towns have been questioned and 57 have been detained in the effort, which began when soldiers found lists of police names in the possession of suspected drug dealers arrested in May.

The police chiefs brought in on Thursday were from the towns of Montemorelos and Allende, Nuevo Leon's state government said in a statement.

Calderon has struggled to combat rising drug violence and corruption, sending 45,000 troops to drug hot spots since taking office in December 2006. More than 10,800 people have since died in drug-related incidents.