Sy Phong had been held in jail without trial as one of two suspected ringleaders of a protest over village land given to a Vietnamese company.
More than 200 officials have been dismissed or warned over bribes or embezzlement since March.
Soil was used instead of concrete, causing the Xe Pian-Xe Namnoy saddle dam to fail in heavy rain, an official report concludes.
Thousands of acres have been granted to banana farms that negotiate with local officials to skirt the ban.
The Siphandone Special Economic development project promises economic growth but pits villagers against developers.
The government has offered live chickens and pigs to villagers who relocated for the Don Sahong dam project.
Vietnam, Laos, Cambodia and Myanmar have retaliated against journalists for government criticism.
A Lao woman says she was misled by traffickers to expect a relatively high-paying job in China, taken across the Lao-China border illegally, and sold to a Chinese man.
The three had handed out religious tracts in Lao villages, and were held under loose supervision for 10 days for questioning.
Police still search for a suspect seen speeding from the crime scene in a car, sources say.