The 28 officers from the town of Ocampo in the western state of Michoacan were arrested Sunday on suspicion of involvement in the murder of Fernando Angeles Juarez.
Juarez, 64, was running as the candidate for the center-left Party of the Democratic Revolution in Ocampo, before being shot dead June 21.
State officials took the cops in for having alleged ties with criminal groups possibly involved in the candidate's killing, El Universal reported.
Public Security Director Venancio Colin was chased out by 16 Ocampo cops in a hail of bullets when he first tried to arrest them Saturday, sources told the paper.
He came back Sunday with reinforcements and arrested the entire force, who were cuffed and taken to the state capital for questioning