All three killings occurred in areas heavily hit by drug cartel violence, but there was no immediate information on the motives in the deaths.
On Thursday, gunmen in a truck opened fire on a campaign rally being held by Enrique Hernandez, a mayoral candidate in Yurecuaro, in the western state of Michoacan.
The state prosecutors' office said the gunfire killed Hernandez on the spot, and wounded three other people. Hernandez was a leader of the town's "self-defense force," one of the vigilante groups that sprang up in 2013 to break the power of the Knights Templar drug cartel in Michoacan.
Yurecuaro is located near the border with Jalisco state, an area where the violent Jalisco New Generation cartel has been expanding its influence, fighting both authorities and rival gangs.