Two key witnesses and forensic ballistics secured the convictions of two American men found guilty on Tuesday in the 2023 murders of a prominent Quebec couple, prosecutors in the Caribbean island nation of Dominica said as they prepared for an expected appeal.

A jury found Jonathan Lehrer and Robert Snyder Jr. guilty of murdering Montreal entrepreneur Daniel Langlois and his partner, Dominique Marchand, who were renowned throughout Dominica for funding philanthropic efforts and constructing a luxury resort.

The trial started on July 1 under a blanket gag order that blocked public reporting on the proceedings.

With the order now lifted, special prosecutor Keith Scotland said ballistics tests provided the clinching evidence in his favour. “They took two spent bullets out of the body of Daniel Langlois and linked it to the gun of Jonathan Lehrer,” he told The Globe and Mail. “That was damming evidence.”

Lawyers for the convicted men did not respond to interview requests.

The couple’s burned remains were discovered on a remote road on Dec. 1, 2023, touching off an extensive police investigation and prosecution that taxed the nation’s limited justice resources before culminating on Tuesday in a courtroom in Roseau, the capital of Dominica.

A jury took two hours to deliberate. Video from local media shows the prosecutors exiting the courthouse to cheers of “Good job” from a small group of locals celebrating the decision.

Early on in the investigation, police theorized that Mr. Langlois and Ms. Marchand were shot in their Nissan somewhere around Bois Cotlette, a cocoa farm owned by Mr. Lehrer. They believed the killers had then driven the Nissan to a mountain road and torched the car with the bodies inside before pushing it off a cliff.

The Canadian businessman and the American cocoa farmer had been entangled in a long-running legal battle over a road that bisected Bois Cotlette and served as the main thoroughfare to Coulibri Ridge, Mr. Langlois’s luxury eco-resort that opened in 2022 and brought much-needed tourist dollars to the hurricane-battered nation of roughly 72,000 people.

Public opinion tended to side with Mr. Langlois, who had founded and sold a pioneering 3D animation company in Quebec, renowned for working on the likes of Jurassic Park and Titanic, before bringing his considerable fortune to Dominica in the late 1990s.

After Hurricane Maria devastated the island in 2017, Mr. Langlois launched an organization called Resilient Dominica, which paid for a school lunch program, provided solar-powered lights for students, funded the reconstruction of a primary school and built a jetty for disaster evacuations.

Shortly after the arrests, locals told The Globe they had little faith in Dominica’s justice system to hold the case together, and worried about Prime Minister Roosevelt Skerrit intervening on behalf of Mr. Lehrer, who was involved in a government Citizenship by Investment program that granted passports to foreign investors.

Mr. Skerrit’s government brought in an off-island special prosecutor, Mr. Scotland, a prominent attorney and member of Parliament from Trinidad and Tobago, to pursue the case.

“We put a great deal of resources into this matter from the time that the individuals were charged,” said Sherma Dalrymple, Dominica’s director of public prosecutions, in an interview. “We did it speedily, we did it properly and we were very much committed to getting a conviction.”

Ms. Dalrymple said testimony from two witnesses formed the backbone of their case, placing the Americans around the crime scene at the time of the slayings.

The first was Norville Williams, a Bois Cotlette employee who was at the scene when the Quebec couple was shot in their car, according to Ms. Dalrymple. His testimony placed Mr. Lehrer at the shooting and gave circumstantial evidence that he drove to the secondary scene, she said.

The second was a German hiker who happened to be at both scenes and testified about an encounter with Mr. Snyder on the road, Ms. Dalrymple said.

A jury trial is the only option under Dominican law. Both Ms. Dalrymple and Mr. Scotland said they anticipate an appeal, which would be adjudicated by a three-judge panel.

“They usually appeal in these cases, but we are sure that we can defend an appeal in this matter,” said Ms. Dalrymple.

Sentencing has been scheduled for September.

Neil Suter, a Canadian construction manager who worked on Coulibri Ridge and befriended the couple, said he will only feel a sense of relief if the appeals process upholds the convictions.

Mr. Suter said the deaths of Mr. Langlois and Ms. Marchand continue to leave a hole in the country.

“What they did in Dominica was truly amazing,” he said. “And it just can’t be replaced in Dominica. They were down-to-earth, amazing people.”