BERLIN (Reuters) - Two years to the day after the Germanwings crash in southern France, the father of the plane’s pilot detailed his doubts that his son intentionally brought down the aircraft to commit suicide and said he was seeking the truth about what happened.

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“In the six years before the crash, we saw our son as a life-affirming and cheerful person. At the time of the crash, our son was not suicidal,” Guenter Lubitz told journalists in a news conference on Friday.

Investigators have concluded that his son, co-pilot Andreas Lubitz, locked the captain out of the cockpit and deliberately flew the Germanwings A320 jet into a French mountainside on March 24, 2015 on a flight from Barcelona to Duesseldorf, killing all 150 people on board.

Prosecutors have said Lubitz was suffering from a mental disorder with psychotic symptoms that led to suicidal thoughts but that he had concealed his illness from his employer, part of the Lufthansa group.

As the families of the crash victims and Lufthansa’s Chief Executive Carsten Spohr paid their respects at the crash site in France on Friday, the pilot’s father and an aviation journalist he hired to help sift through investigators’ files said there was no conclusive evidence dispelling his doubts over what had happened.

The journalist, Tim van Beveren, said there was no evidence showing why the other pilot was unable to get back into the cockpit, that turbulence may have forced Lubitz to fly at lower altitudes and it has not been proven that Lubitz was conscious during the descent.

He said he did not have an alternate theory as to what caused the crash but said further investigation was necessary.

Lubitz, who spoke to the media for the first time since the crash this week, said it had hit him and his family hard that prosecutors declared within days of the crash that his son had brought down the plane on purpose.

“We had to live with the fact that he was portrayed as a mass murderer in the media,” he said as he addressed journalists, dressed in a dark suit and tie.

Asked whether he believed his son was innocent, he said: “We are searching for the truth.”

Lufthansa said earlier this week there was no reason to doubt the findings of the investigators.

German prosecutors decided earlier this year that nobody other than Lubitz could be held accountable for the crash and repeated that stance this week.

Duesseldorf-based prosecutor Christoph Kumpa said he saw no reason for the prosecution to resume its investigation.

“The crash happened due to the deliberate actions of the co-pilot, likely with suicidal intent. There is not sufficient actual evidence of any other cause of the crash, and none is foreseeable,” he told Reuters ahead of Friday’s news conference.