Now even the FBI has confirmed that he is a Pakistani. What more proof do you need ?
As far as getting access is concerned, the Pak High Commission should respond to his letter first and establish a line of communication.
First and most important should be access to Ajmal for Pakistani Consulate Gen which India has flatly denied. If he is a Pakistani Citizen (as India claims), then Pakistani Diplomats should have access to him by all rules and standards. No country can work on "he said, she said lists".