RIO DE JANEIRO, Oct. 9 — An Argentine tribunal sentenced a Roman Catholic priest to life in prison on Tuesday for conspiring with the military in murders and kidnapping during the country’s “dirty war” against leftist opponents, in a case that has become for many a powerful symbol of the church’s complicity with the former regime.

The Rev. Christian von Wernich, who worked as a police chaplain during the military dictatorship, was found guilty of involvement in seven murders, 31 cases of torture and 42 kidnappings. He is the first Catholic priest prosecuted in connection with human rights violations in Argentina, where at least 12,000 people were killed during the military regime from 1976 to 1983.

Seconds after the sentence was read, hundreds of protesters cheered and fireworks were shot off outside the courthouse in La Plata, about 50 miles from Buenos Aires. Father von Wernich, who wore a bulletproof vest in court, clasped his hands and frowned.

Image The Rev. Christian von Wernich Tuesday in La Plata. Credit... Natacha Pisarenko/Associated Press

Nearly a quarter of a century after the junta was toppled in 1983 and democracy was restored, the trial of Father von Wernich has forced Argentina to confront the church’s dark past during the dirty war. It illustrated how closely some Argentine priests, who had strongly aligned themselves with the power of the military, worked with the regime’s leaders.