A man facing criminal charges for torching a cathedral in western France last year was arrested Monday for allegedly killing a Catholic priest, an episode that is already stoking a fierce political debate over migration laws after reports identified the suspect as an undocumented immigrant who had faced expulsion from the country.

The Diocese of Luçon said the slain priest was Father Olivier Maire, head of the Montfortain Missionary Order in the small town of Saint-Laurent-sur-Sèvre. Local police released few details in the incident’s immediate aftermath, but news of Maire’s death quickly reverberated around the nation, which prizes its secularism — or laïcité — but remains predominantly Catholic.

French President Emmanuel Macron praised Maire’s love and generosity.

“On behalf of the Nation, I pay tribute to Father Olivier Maire,” Macron said on Twitter. “Warm thoughts for the Montfortains and all Catholics in France. Protecting those who believe is a priority.”

The country’s interior minister, Gérald Darmanin, was among the first to announce Maire’s killing, calling it a “dramatic assassination” and saying he would travel to the region.

The suspect, a 40-year-old man from Rwanda, had been living with Maire’s order while he awaited trial after confessing to setting the fire that burned through a cherished Gothic cathedral in Nantes roughly one year earlier, said Yannick Le Goater, a deputy prosecutor. The suspect had recently discussed leaving the order’s premises, where he was under judicial supervision, and had been transferred to a psychiatric hospital until the end of last month, Le Goater said. It was unclear where the suspect was this month. He turned himself in to police Monday morning.

The suspect’s attorney did not respond to a request for comment.

The man’s immigration status quickly became the target of France’s far-right politicians, who have pushed a fervently anti-immigrant message and have sought to portray Macron as weak on security ahead of the 2022 presidential election.

Their standard-bearer is Marine Le Pen, head of the National Rally party and seen as Macron’s primary competitor in the April contest. On Monday, she tweeted that Maire’s death marked a “total failure” of Macron’s government.

“So in France you can be an illegal immigrant, torch Nantes cathedral, never be expelled and reoffend by murdering a priest,” she wrote. “What’s happening in our country is unprecedented: the total failure of the state.”

Darmanin chastised Le Pen for advancing “a polemic without knowing the facts,” and said that authorities were not able to deport the suspect because he was being held under judicial supervision ahead of his trial for the cathedral fire. At a news conference hours later, Darmanin called the criticism a “useless controversy.”

Bruno Retailleau, a conservative senator who has represented the region for more than 15 years, said he knew Maire well and called him a kind man who was “murdered by a criminal he was sheltering out of charity.”

“But what was this individual still doing in France?” Retailleau asked in a tweet.

Maire’s death is the latest in painful blows to the country’s Catholic community in recent years.

The July 2020 fire at the Cathedral of St. Peter and St. Paul, in the heart of Nantes, traumatized many — not only for the destruction it wrought on the grand 15th-century building, but also because it brought scenes reminiscent of the 2019 inferno that nearly destroyed Notre Dame in Paris.

That blaze was mourned as a national tragedy and Macron said then that Notre Dame was a metaphor for all of France.

“Notre Dame is our history, our literature, our imagination,” he said.

And in 2016, two followers of the Islamic State entered a church in Normandy and killed an 85-year-old priest who was celebrating morning Mass.

Prosecutors on Monday said they were not investigating Maire’s killing as an act of terrorism.

Tributes to the 60-year-old priest poured in from across the country.

Laurent Percerou, the bishop of Nantes, said in a statement that Maire was benevolent, a good listener, and that by taking in the suspect after the fire, he was “faithful to his religious consecration and to the founder of his congregation.”

Pierre-Hervé Grosjean, a priest in the diocese of Versailles, wrote of Maire’s death: “The emotion is strong, shared by all, believers or not.”

Thebault reported from Brussels. Rick Noack in Paris contributed to this report.