Acapulco's former mayor has been given 72 hours to explain why hundreds of police weapons have gone missing.
The entire municipal police force in the coastal Mexican resort was suspended last week amid suspicions of infiltration by criminal groups.
The early stages of an investigation have shown that 342 of its weapons are unaccounted for.
The defence ministry has deemed ex-Mayor Evodio Velázquez Aguirre responsible as he signed for them.
Mr Velázquez Aguirre, whose term ended at the weekend, has called the government-led investigation a publicity stunt, according to local media.
Marines raided the municipal police headquarters last Tuesday, disarming 700 officers. The federal police and the military have since been tasked with patrolling the city while an investigation is carried out.
Acapulco became famous as a destination for the rich and famous in the 1950s and 1960s but has since become a hotspot for drug trafficking and has a high murder rate.
How bad was the situation?
The raid came after state officials noticed an increase in crime in Acapulco and "a lack of action by the police to deal with it".
Last year, the homicide rate in the city rose to 106 murders per 100,000 inhabitants, one of the highest in the world. London by comparison had a rate of 1.45 murders per 100,000 people between September 2016 and September 2017.
In January, the US state department prohibited US government employees from travelling to Acapulco and surrounding Guerrero state.
What's the situation in the rest of Mexico?
Acapulco is one of the most violence-stricken cities in Mexico and is located in a state which has been badly affected by drug-related violence.
And while many parts of Mexico remain largely peaceful, the murder rate nationwide reached a record level last year.
Municipal police forces are seen as the weakest link in Mexico's security system. Poorly trained and badly paid, they can easily be threatened or cajoled into colluding with local drug gangs.
Federal police and soldiers have taken over policing duties in some crime hotspots before but the move has failed to drive down crime for good.
Human rights groups have also warned that while marines and soldiers have had success in arresting top drug dealers, they are not trained for policing duties and can be heavy handed when dealing with civilians.