Q. Thank you for getting back to me, let me rephrase the question.
A non-Jew that was a very religious dedicated Catholic for many years (actually a priest) and decided to convert to Judaism, since he argues that finally he saw the real truth. Can he be trusted that he has really abandoned his former strong beliefs, since he may even be deceiving himself, and besides he does not have a chezkas kashrus yet? What is Horav Miller’s opinion in regards a Beis Din accepting him as a ger?

A. Horav Shlomo Miller’s opinion is that teshuva is open in principle to all, and the truth is to be found in the depths of the hearts of all human beings.
The Rov suggested that in this particular case the gerus candidate should be offered a priori the easier option of becoming a Ger Toshav, or a Noahide who keeps the seven mitzvos. If he is adamant and insists to becoming a full fledged Ger Tzedek, more preparatory time should be requested from the applicant. (some Batei Din as is have a five year waiting period).
The Rov added that a precise and clear expression of denial of his prior beliefs should also be requested by the Beis Din.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a