A French psychiatrist has been found guilty of manslaughter after one of her patients hacked an elderly man to death, in a landmark ruling that could have a major impact on the care of mentally ill patients in France.

Danielle Canarelli, 58, a doctor with 30 years' experience, based at the Edouard-Toulouse hospital in Marseille, was given a one-year suspended prison sentence because judges said she had committed the "grave error" of failing to recognise the public danger posed by her patient, Joël Gaillard.

Gaillard, 43, who is now said to suffer from a kind of paranoid schizophrenia, had been treated by Canarelli for four years, between 2000 and 2004. In February 2004, during a hospital consultation with her, he escaped. He went to Gap, in the Alps region, 20 days later and used an axe to kill Germain Trabuc, 83, his grandmother's partner, reportedly under an illusion that his inheritance was threatened by Trabuc.

Gaillard fled the scene of the crime but later was hurt as he tried to break into a building, after which he went to a hospital casualty department to be treated. Police were alerted and arrested him there.

Trabuc's son, a local authority worker, decided to take legal action against the psychiatrist after Gaillard was found criminally irresponsible for his actions because of his mental health and the case against him was dropped.

In their ruling against the psychiatrist, the judges said Canarelli had failed to properly evaluate the danger posed by her patient, who had been forcibly committed to a secure hospital on several occasions for a series of increasingly dangerous incidents, including a knife attack, arson and an attempted murder.

The court said Canarelli should have requested Gaillard be placed in a specialised medical unit or referred him to another medical team, as one of her colleagues had suggested. Her refusal had amounted to a form of "blindness", the court president, Fabrice Castoldi, said. He stressed that "we are not judging psychiatrists or the psychiatric profession, but a particular case".

As well as the suspended prison sentence, the psychiatrist was ordered to pay €8,500 (£6,920) to the victim's children.

Defence lawyers warned the ruling would have serious repercussions for treatment of the mentally ill. "If a psychiatrist lives in fear of being sentenced, it will have very real consequences and probably lead to harsher treatment of patients," Canarelli's lawyer, Sylvain Pontier, said. His client was likely to appeal.

SPEP, the union for French state psychiatrists, which backed Canarelli during the trial, said the landmark verdict was worrying and risked scapegoating the profession over a complex case. The union said Canarelli had notified police and other authorities after her patient's escape. On the first day of the trial, psychiatric medical staff had protested outside court with banners, including one reading: "Dark day for psychiatry".

Outside court, the victim's son, Michel Trabuc, said he hoped the case would set a precedent. "There's no such thing as zero risk, but I hope this will move psychiatry forward and, above all, that it will never happen again," he said.

Earlier he had told the newspaper Le Dauphiné Libéré how on the day of the attack he had been called by his father's neighbour. He went to the scene to find his father lying under a sheet. "His arm was hanging out from under the sheet. I can still see it. I still see it at night." He said that when the case against Gaillard was dropped because he was not criminally responsible "it was like saying nothing had happened, that we'll forget someone had died". He said he had brought the case to protect "the memory of my father".

Gaillard is currently receiving psychiatric treatment at another hospital. Canarelli's lawyer said he had since married and had at least one child.

In a frontpage editorial, Le Monde called the judges' ruling "courageous".

Dr Trevor Turner, a consultant psychiatrist in east London and a former vice-president of the Royal College of Psychiatrists, said: "I entirely sympathise with her [Canarelli] and her colleagues as to the difficulty they find themselves in when asked to make these predictions [about their patients' future behaviour]."

He added: "In this country, there is no one, as far as I know, who has been charged with that kind of thing."

In the 1970s, a psychologist who had been treating Prosenjit Poddar, a student at the University of California at Berkeley, was held liable by the California supreme court for failing to warn Poddar's girlfriend, Tatiana Tarasoff, that he intended to kill her, as Podder had told the psychologist in therapy he intended to do.

"Psychiatrists rushed about rounding up their patients," said Turner. They looked for reasons to put them in institutions. "It set up a lot of concerns as to risk management and risk assessment."

Psychiatrists in the UK have not been held to account by the courts, but have for years been subjected to murder inquiries, which are statutory whenever somebody with mental illness carries out a killing. These are tribunals led by a lawyer and another psychiatrist that investigate the care the killer received. Often the doctor is criticised, by the inquiry and then the press.