Gunmen opened fire at a wedding in western Mexico, killing one man on the spot while three other people were later shot dead as medical workers treated them, prosecutors said.
Two shooters, identified by witnesses as the sons of a local police chief, burst into the wedding party in the village of Cungo late on 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 recognised the sons of the Salvador Escalante municipal police chief, a group of 50 local residents organised 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.