WROCLAW, Poland — A court yesterday convicted an author of directing the killing of a businessman in a crime that bore eerie similarities to a murder he described in a novel three years later.

The court ruled that Krystian Bala planned and directed the grisly killing of Dariusz Janiszewski, but said there was insufficient evidence to convict him of carrying out the murder himself. He was sentenced to 25 years in prison.

“The evidence gathered gives sufficient basis to say that Krystian Bala committed the crime of leading the killing of Dariusz Janiszewski,” Judge Lidia Hojenska said. “He was the initiator of the murder; his role was leading and planning it.”

Judge Hojenska said it was not clear who actually killed Janiszewski and who might have aided Mr. Bala in the crime, but that the evidence overwhelmingly pointed to Mr. Bala’s involvement in the events that led to Janiszewski’s disappearance.

Mr. Bala, 34, sat stone-faced between two policemen as Judge Hojenska read the verdict. Mr. Bala’s family and lawyer said they planned to appeal.

“Justice was served, but the verdict will never be adequate to the crime,” said Janiszewski’s father, Tadeusz, who held a photo of his son during the hearing. “It’s tough to talk about being happy with it because nothing will bring my son back.”

Fishermen dragged Janiszewski’s corpse — stripped to a shirt and underwear — from the muddy banks of the Oder River in southwestern Poland on December 10, 2000. His body showed signs of starvation and torture. His hands were bound behind his back and tied to a noose around his neck.

Police quickly identified the victim as Janiszewski, who had disappeared four weeks earlier. But they struggled to dig up clues and dropped the case after six months. Five years later, a tip led them to Mr. Bala’s 2003 novel, “Amok,” an alcohol- and sex-fueled tale narrated by a man named Chris, who stabs a woman after binding her hands behind her back and then running the rope to a noose around her neck. The similarities aroused investigators’ suspicions, although the parallels were not part of their case to the panel of judges.

The judge said Mr. Bala was driven by jealousy to kill Janiszewski, whom Mr. Bala suspected of having an affair with his estranged wife.

“He was pathologically jealous of his wife,” the judge said. “He could not allow his estranged wife, whom he treated as property, to have ties with another man.”

Mr. Bala argued that he had never met or talked to Janiszewski.

Judge Hojenska said a host of circumstantial evidence led the court to its verdict.

Police had tracked down a phone card used to make calls from a public phone to Janiszewski’s office and then to his cell phone the morning he disappeared. Calls were made the same day using the same card to Mr. Bala’s girlfriend and his parents.

Prosecutors also said that someone using Mr. Bala’s account on an Internet auction site sold Janiszewski’s cell phone four days after his disappearance. Mr. Bala could not explain that.

In 2003, a Polish TV show on unsolved crimes broadcast a segment on Janiszewski’s murder. Soon after the clip aired, the program’s Web site dedicated to the case received hits from computers in Singapore, South Korea, and Japan. Prosecutors say Mr. Bala was visiting those countries on the dates of the Web site hits.