Mr. Simbikangwa, a cousin of President Juvénal Habyarimana of Rwanda — whose death in a plane crash touched off the genocide — was said to have had close ties with death squads as well as with the Akazu, a secret and elite Hutu corps within Mr. Habyarimana’s inner circle. He was also a shareholder of the Radio des Milles Collines, which spread fierce anti-Tutsi propaganda across the country before and during the slaughter.

Many French lawyers have emphasized the difficulty of prosecuting a case involving events that took place 20 years ago and 3,800 miles from France. Many Rwandan witnesses at the trial had trouble recounting what they saw between April and July 1994, when 800,000 people were killed. Some witnesses said they feared reprisals in their country.

Still, many witnesses provided chilling accounts of their encounters with Mr. Simbikangwa.

“On April 7 in the afternoon, Pascal Simbikangwa came to a meeting in Kibihekane where an attack was prepared,” said Théoneste Habarugira, a former member of the Interahamwe who spent seven years in prison. “He said that we had to kill the Tutsi.” Mr. Habarugira and other witnesses described Mr. Simbikangwa as an influential officer who supervised several roadblocks.

Valérie Bemeriki, one of the most prominent voices on Radio des Milles Collines, said Mr. Simbikangwa “had organized the genocide.” She testified by video from a prison in Kigali, where she is serving a life term.

Other witnesses defended him, emphasizing his ability to protect people he knew even as he was ordering the deaths of their fellow tribesmen. Former Tutsi neighbors of Mr. Simbikangwa described taking refuge at his house. “Pascal had a right over life and death,” said Isaie Harindintwari, who lived opposite Mr. Simbikangwa in Kigali. “I was untouchable because I was his Tutsi.”

Mr. Simbikangwa denied all the charges against him, arguing that he was then a second-rate official in the presidential intelligence service who believed that the threat did not come from the Tutsis but from the Tutsi-dominated Rwandan Patriotic Front, a rebel group.

At one point during his trial, Mr. Simbikangwa, whose mother and wife were Tutsi, denounced what he called the calumny and defamation directed at him.

“Telling moribund, absurd, negative things against the people I have protected seems to go against the honor of a military man, against my notion of how one treats a human being, and against the attachment I had for my mother, and the mother of my daughter,” Mr. Simbikangwa said.