Soldato
All seems very vague, if they have something then it still needs to be substantial to say that it's concrete evidence. If it isn't forensic, then it almost certainly has to be photo/videographic and that's likely why it can never be shared.
They discovered approx 8,000 photos videos of child abuse when they searched his motorhome in May 2016, but they were looking for Inga Geriche and may not have connected it to this case. I wonder if they've gone back over this evidence and have a made a connection.
Or perhaps her DNA in the motorhome.
That would be direct forensic evidence linking him to the disappearance/murder.