BARCELONA, Spain — Doctors who treated Germanwings pilot Andreas Lubitz for depression and mental illness before he killed 150 people by crashing into the Alps last year refused to speak with French investigators who were trying to prevent a similar sequence from ever happening again, one victim's father said Saturday.

The French investigators told relatives at a meeting in Barcelona that the German doctors were not required to talk about Lubitz's medical conditions under German privacy laws and they didn't, even though the 27-year-old also died in the March 24, 2015 plane crash.

The experts from France's BEA crash investigation agency did obtain detailed German medical records about Lubitz but "they emphasized that the doctors, those who treated him, refused to give any information," said Robert Tansill Oliver, who attended the Germanwings relatives' meeting.

The French investigators told the relatives that one of their safety recommendations would be a requirement that doctors provide authorities with information about pilots' mental health issues.

The BEA on Saturday declined to comment on the closed-door meetings with relatives, who were shown a slide show but given no written materials.

The meetings Saturday in Barcelona and Bonn briefed the victims' relatives about a BEA report being released Sunday that is expected to make recommendations to help aviation agencies and airlines around the world prevent similar crashes. Most of the victims of Flight 9525 from Barcelona to Duesseldorf were from Spain and Germany.

Germanwings and Lufthansa have strongly denied any wrongdoing in the crash, insisting that the co-pilot was certified fit to fly. In the months before the crash, Lubitz visited 41 doctors, and none warned his employer or authorities that Lubitz might be too ill to fly. Germany's confidentiality laws prevent sensitive personal information from being widely shared, although the law allows doctors to suspend patient privacy if they believe there is a danger to the person's safety or that of others.

Oliver's 37-year-old son, Robert Oliver Calvo, died in the crash, leaving behind a wife and two children. His son was an American who lived in Spain and managed real estate for the Barcelona-based clothing chain Desigual.

Investigators say Lubitz deliberately crashed the plane into a French mountainside. He had previously been treated for depression and suicidal tendencies and documents seized by prosecutors show he partly hid his medical history from employers.

The BEA representatives told victims' relatives in Barcelona "they would have liked to have talked to the doctors who treated Lubitz to understand why he acted in such a suicidal way. They wanted to understand why a young pilot with supposedly a nice family life would want to commit suicide," Oliver Calvo's father said. "They wanted to find out why he did what he did, the root causes."

Oliver, a retired teacher who is also American and lives in a Barcelona suburb, said relatives at the meeting were told about Lubitz' mental health problems, including a psychotic depressive episode. Some of this information was forwarded to Germanwings, his employer, while other data was not, Oliver said.

Oliver said relatives at the meeting in Barcelona "were really upset."

"People were not happy at all with some of the explanations. Some of the family members felt as if these BEA representatives were Lubitz' lawyers — making excuses as to why Germanwings didn't take action knowing what they knew," he told The Associated Press.

"How is it possible Germanwings would let a crazy guy fly a plane? He was mentally unbalanced, tremendously unbalanced," he added.

No mention was made of a media report that one of Lubitz's doctors two weeks before the crash thought he should not fly but did not give the information to authorities, Oliver said.

In Bonn, Christof Wellens, a lawyer for some victims' families, said they had questions about "how is it possible that such an ill person gets a pilot license?"

Investigators said one of their recommendations is for more transparency between doctors who treat pilots and the airlines they work for, Oliver said, adding that the victims' relatives could not understand why the doctors refused to speak with the French investigators.

"Everyone in the auditorium was asking the same question: 'Why did these German doctors refuse to talk to you?" he said.

Oliver said he feared there may never be clarity over why Lubitz crashed the plane unless his German doctors agreed to be interviewed. He said he believed that Germany needs to change its laws to make sure that doctors who treat pilots are required to talk to investigators in the future.

"How did he fall through the cracks? The controls did not work," Oliver said. "You listen to this information and you wonder, 'Am I safe to fly on a plane?'"