WASHINGTON—Former Peruvian President Alberto Fujimori was sentenced to 25 years in prison this week by Peru’s Supreme Court in connection with two massacres committed by a death squad known as the Colina group, as well as the kidnapping of a journalist and a businessman. The precedent-setting trial, which international observers have said met high standards of due process, establishes the responsibility of those who govern over dirty wars conducted without written orders.

Between 1991 and 1992, the Colina group, an army detachment charged with combating the terrorist organization Shining Path, killed at least 50 Peruvians in nine separate actions. Fujimori’s trial focused on two of them—the deaths of 15 people in November 1991 during a barbecue in the poor Lima neighborhood of Barrios Altos, and the kidnapping and killing, in July 1992, of nine students and a professor from La Cantuta University. Fujimori contended that the absence of written or audiovisual proof that he had given the orders warranted his acquittal.

But prosecutors built a devastating case demonstrating Fujimori’s responsibility for the strategy, the operational structure and the political cover-up related to the Colina group’s activities. The key figure in unlocking the case was Vladimiro Montesinos, a jailed army captain with a history of treason who would never have commanded the colossal power that he did without the only person who could delegate it to him—Fujimori himself.

Military witnesses testified that soon after coming to power, Fujimori ordered the implementation of a new antiterrorist strategy based on the use of the National Intelligence Service and the appointment of Montesinos as its de facto head. Fujimori put two secret funds under Montesinos’ control and authorized him to coordinate the activities of all the military intelligence services. Various testimonies confirmed the authenticity of two army manuals describing the need to create “special operations” teams authorized to kill. Eight members of the Colina group admitted killing suspects and that Montesinos was directly involved with the crimes of Barrios Altos and La Cantuta: In one case he gave a verbal order and in the second he discussed the killings with the head of the army soon after they took place.

In 1991, before the creation of the Colina group, Fujimori recommended in writing that its future members, assigned by Montesinos to infiltrate the police, be promoted. That same year, the president accompanied troops as they entered La Cantuta University to establish a base there. A year later, soldiers from that base would collaborate with Colina in the kidnapping of the nine students and the professor.

Months after the Colina group was formed, the head of the army, appointed by Fujimori at Montesinos’ request, held a party in honor of the death squad and told its members that they constituted “the invisible part” of the antiterrorist strategy. In an interview after the collapse of the Fujimori regime, the head of Colina explained the chain of command: “A decision was made by those who governed the country and everything that happened must be interpreted as part of a decision made by the president.”

When the crimes became public, Fujimori denied they had taken place. When evidence surfaced, he denied Montesinos and the army chief had anything to do with them. Under international pressure, the regime tried some Colina members in a secret military tribunal. They stayed in an army barracks for months until they were granted amnesty.

Ultimately, the defeat of Shining Path had nothing to do with the Colina group—whose victims were not even affiliated with Shining Path—but with the activities of a special police unit that captured the Maoists’ leader in 1992.

It is extraordinarily fitting that, despite the disruptive actions carried out by Fujimori’s party since he was extradited to be tried for human rights violations and corruption, and the campaign of intimidation against the prosecutors, the families of the victims and the judges, the court handed him a long sentence.

The decision should set a precedent for future trials in which political leaders who are responsible for destroying a country’s institutions and rule of law seek to evade responsibility by hiding behind the absence of material proof of their involvement in dirty wars. In many ways, the history of Latin America has been one succession of strongmen who did just that. Fujimori’s sentence sends the message that that tradition does not have to be honored forever.