This is confusing to me a little. If your Dad collected the car from the street when it was found, did LE process the car in the street? I thought they found the car on the 5th and didnt tell anyone? I had imagined they took it back to the station at that time for forensics but now I am wondering again. Regarding the iphone 7 adaptor, hopefully LE have looked at it for prints. Perhaps J had a third phone and has ditched the other two?
But I understood it the father went down when it was collected on the street but was told not to tell anybody.
As to the fingerprints, I would think touch DNA would be best also as a consideration.