PHNOM PENH, Cambodia — A United Nations-backed tribunal on Monday found a 67-year-old former prison warden of the Khmer Rouge guilty of crimes against humanity and war crimes for overseeing the torture and killing of more than 14,000 prisoners. He was the first major figure to be tried in the murderous regime since it was toppled 30 years ago.

But in a sentence that was likely to be considered shockingly lenient here, the court sentenced him to serve 19 years in prison — 35 years minus 16 years for time already served. Prosecutors had sought 40 years. There is no death penalty in Cambodia.

The defendant, Kaing Guek Eav, commonly known as Duch, had admitted in an eight-month trial to many of the accusations against him. He oversaw a system that came to symbolize a regime responsible for the deaths of 1.7 million people from 1975 to 1979.

Dressed in a blue button-down shirt, sipping sometimes from a glass of water and carrying what appeared to be a Bible, he listened impassively as a judge read out the charges and verdict against him. The packed courtroom included some survivors of the prison he ran — three of whom had testified about the torture inflicted upon them.

The tribunal, which began work in 2006, now moves to “Case Two,” for which four high-ranking Khmer Rouge officials are in custody awaiting trial sometime next year. The Khmer Rouge leader, Pol Pot, died in 1998.

Duch’s own plea was unclear. On the final day of the trial, in November, he unexpectedly asked to be set free, seeming to contradict a carefully constructed defense in which his lawyers sought to minimize his sentence through admissions of guilt mixed with assertions that he was just one link in a hierarchy of killing.

“I am accountable to the entire Cambodian population for the souls that perished,” he said at one point. “I am deeply remorseful and regret such a mind-boggling scale of death.”

But he added: “I ended up serving a criminal organization. I could not withdraw from it. I was like a cog in a machine. I regret and humbly apologize to the dead souls.”

Many of his victims, along with outside observers, questioned the sincerity of his remorse, particularly as it was coupled with a sometimes aggressive and arrogant demeanor in the courtroom and evasiveness regarding many specific allegations.

Despite those doubts, David Chandler, a historian of Cambodia, noted that Duch was the only one of the five defendants to have admitted guilt.

“He’s a guy who’s thought about it, faced up to some stuff,” said Mr. Chandler, the author of “Voices From S-21,” a book about the prison, known as S-21 or Tuol Sleng. “Duch is the only human on trial. The others are monsters.”

A former schoolteacher, Duch took obvious pride in the efficiency of his operation, where confessions — some of them running to hundreds of typed pages — were extracted by torture before the prisoners were sent in trucks to the killing fields.

He disappeared after the Khmer Rouge was driven from power by a Vietnamese invasion and was discovered in 1999 by an Irish journalist, Nic Dunlop, living quietly in a small Cambodian town, where he said he had converted to Christianity.

At one point in his testimony, in an extravagant display of contrition, Duch appeared to compare himself with Christ.

“The tears that run from my eyes are the tears of those innocent people,” he said. “It matters little if they condemn me, even to the heaviest sentence. As for Christ’s death, Cambodians can inflict that fate on me. I will accept it.”

It is more common among Cambodians — most of whom are Buddhists — to believe in spirits. Tuol Sleng is now a museum, and when part of its roof collapsed last week during a storm, some people said the ghosts of the dead were crying out for justice.

Running parallel with courtroom testimony, the tribunal has faced criticism as it tries to apply international standards of justice within a flawed Cambodian court system.

“The court has struggled to deal with allegations of kickbacks involving national staff, heavy-handed political interference from the Cambodian government, bureaucratic inefficiency and incompetence, and disturbing levels of conflict between international and national staff,” said John A. Hall, a professor at the Chapman University School of Law in Orange, Calif., who has been monitoring the trials.

“Indeed, perhaps one of the most surprising things so far is that the tribunal has not collapsed,” he said.

In an innovation, the trial made room for about 90 “civil parties,” who registered to apply for reparations and were represented in court by lawyers who acted as additional prosecutors.

“For 30 years, the victims of the Khmer Rouge waited while a civil war raged, international actors bickered and the leaders of the Khmer Rouge walked free,” said Alex Hinton, director of the Center for the Study of Genocide, Conflict Resolution and Human Rights at Rutgers University in New Jersey. “Now, for the first time, one of them has been held accountable. The importance of this moment can’t be underestimated.”

But over the years, Cambodia has moved on, with new generations, new concerns and new horizons. Many young people know little about the Khmer Rouge era, and many older people have chosen to forget.

“I go around the country and not a lot of people ask about the trial,” said Ou Virak, president of the independent Cambodian Center for Human Rights, which holds forums on issues of concern to the public. “Not even my mom — and my dad was killed by the Khmer Rouge.”