Two shooters, identified by witnesses as the sons of a local police chief, burst into the wedding party in the village of Cungo late Monday, Michoacan state attorney general Placido Torres told reporters.
"They repeatedly shot a man who was sitting at a table but then the assailants inexplicably shot at the other guests before fleeing," Torres said.
One man was killed and seven others were wounded at the party.
A sport utility vehicle, escorted by a police car, was taking three of the wounded men to be treated elsewhere when an ambulance found them.
As ambulance workers began caring for the wounded, a group of gunmen arrived and killed the trio, Torres said.
After witnesses recognized the sons of the Salvador Escalante municipal police chief, a group of 50 local residents organized a lynch party and headed to the two men's home.
But federal police arrived and the two suspects were taken into custody.
Michoacan is the scene of a violent turf war between Mexico's drug cartels, but it is also known for land disputes between state residents.