Mayoral candidate Fernando Angeles Juarez, 64, was shot dead on Thursday.
Twenty-eight police officers in the town of Ocampo — the entire department — were arrested on suspicion of involvement in the murder.
The candidate was the third politician to be killed in the Mexican state of Michoacan in eight days.
The entire police force of a Mexican town has been arrested on suspicion of involvement in the murder of a local mayoral candidate.
Fernando Angeles Juarez, 64, was shot dead on Thursday. He was running as the candidate for the centre-left Party of the Democratic Revolution in Ocampo, Michoacan, which has a population of 24,000.
All 28 police officers from the town were arrested after the killing, a state source familiar with the investigation told the Reuters news agency .
Google Maps/Business Insider
A statement from state authorities on Sunday said that the officers were being questioned by police internal affairs official. The statement did got give further details beyond stating that the investigation was focusing on violations of the police's code of conduct.
Silvano Aureoles, the governor of the state, instructed the attorney general to begin investigating the death, he tweeted on June 21.
The arrested officers will appear before the Internal and Legal Affairs Commission of the Deputy Office of Public Security, according to Mexican newspaper El Universal.
Angeles Juarez was the third politician to be killed in the state in eight days.
His party, el Partido de la Revolución Democrática, condemned the violence in Mexico in a statement, calling for the end of murders and for people to be able to vote safety in the country's elections.
More than 100 politicians have been killed across the country in the lead up to general elections on July 1, when Mexico will vote for a new president as well as hundreds of other federal and state positions.