TWT
I am not sure that there is no direct evidence, but I am sure that it has not been made public if it exists. There is no doubt that the facts strongly indicate that this was a murder suicide by the F/O, but further facts are required to confirm this theory.
Clearly, the new revelations regarding the mental problems that the F/O was suffering go along way towards explaining his actions and a possible motive.
It would be interesting to know what drugs he was prescribed or were found at his home. It may be that he ODed on his meds.... this would explain his "laconic" interaction to the landing briefing...
I would not like to jump to the conclusion that he deliberately killed the passengers and crew; certainly the family and friends of the victims will not find it any easier to bear knowing that it was a callous brutal act of murder.