CAROLINA, Puerto Rico — Before the sun rose on the first day of 2018, someone called 911 to report the charred, bullet-riddled body of a man with a snake-like tattoo on his left hand, lying beside a road in the Puerto Rican town of Vega Baja.

The next day, two men were found dead with their feet and hands bound in Bayamon, a working-class city southwest of the capital. Another man was shot to death before dawn in nearby Vega Baja while trying to stop thieves from stealing his generator.