Günter Lubitz has organised a press conference to insist investigators failed to examine all possible angles to the March 24, 2015, crash that killed 150 people.
Prosecutors claim Andreas Lubitz, 27, locked the captain out of the cockpit before he drove the Germanwings flight 9525 into the ground.
And, evidence appears to back their theory.
However, the co-pilot's family is now insisting he was innocent and are presenting their own case.
Father of Germanwings pilot insists investigators have not looked at all possibilities
We would like to say that our son did not suffer from depression on that day
The family revealed they chose to deliver the press conference on the second anniversary of the crash on purpose.
Mr Lubitz said: "Of course we knew that today is the 2nd anniversary, of course we expected people to take it badly that we chose this day.
"I'm sure no matter which day we would have chosen, the reaction would be the same
"We didn't choose this day to hurt the families of the victims but to chose a day that was best for what we want to achieve.
"We would like to say that our son did not suffer from depression on that day."
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The press conference is being live streamed from Berlin
Journalist, Tim van Beveren, has been assisting the family.
He is described by some as "an internationally recognised aerospace expert".
At the press conference Mr van Beveren blasted the evidence.
He said: “Sometimes it takes years for incidents like this to be solved, sometimes they are never solved.
“Therefore I was even more surprised when two days later, I repeat two days, I heard that it was him, that Lubitz was guilty, the co-pilot did it, without mentioning any doubts.
“I’ve never experineced something like this before in my career.”
Tim van Beveren, has been assisting the family with their new theory
The investigator said the black box was found but it was only days later, under a rock, the “chip” from inside was discovered.
The expert said it was "possible" Lubitz was guilty, but that that can only be determined by a proper examination of the evidence.
He said: "It is possible and if it is true that he did fly this plane into the mountain then it is a heavy and difficult truth but that would also be accepted by the Lubitz family, but to date there is no clear evidence.
"Everything is just speculation."
German investigators found Lubitz made inputs into the aircraft’s autopilot ordering it to make a rapid descent when they looked at the data recorder.
Captain Patrick Sondenheimer, had left the flight deck to go to the toilet.
Chilling images depict the Germanwings crash Fri, March 24, 2017
The crash was deliberately caused by the co-pilot, Andreas Lubitz, who had previously been treated for suicidal tendencies and declared 'unfit to work' by a doctor
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Rescue workers and gendarmerie continue their search operation near the site of the Germanwings plane crash near the French Alps on March 26, 2015 in La Seyne les Alpes, France
The voice recorder picked up sounds of him hammering on the door – and while Lubitz does not answer – his breathing can be heard.
Mr Lubitz, 63, remains unconvinced his son had any intention to die.
He said: "Up to now, everyone has believed the theory of a co-pilot who was depressed for a long time, who deliberately crashed his plane into a mountain in a planned act.
"We are convinced this is false."
The lawyer representing several of the victims' families, Elmar Giemulla, said Mr Lubitz was waging an "irresponsible" campaign that would be rip open old wounds.
Giemulla told the Rheinische Post newspaper: “I imagine that Mr Lubitz wants to promote a theory that would absolve his son of any responsibility."
Andreas Lubitz allegedly locked the pilot out of the cockpit
Mr Lubitz said: "What I will tell you now, I do with great care as it is easily misunderstood. My grief is different. It is a certain kind of grief. It is different from the grief of the other relatives.
"We do not just have to live with the loss of our son but that just two days later he was portrayed as a depressive mass murderer. We have to live that whenever there is a terrible attack in the world our son is also mentioned."
The father of the alleged killer also claimed his son's "episode of depression" was over by the time he took the flight.
The plane smashed into the French Alps killing all on board
There were 144 passengers and six staff onboard Airbus A320 from Barcelona to Duesseldorf.
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