I was at Anime North this year and Ryo Horikawa (voice of Hattori Heiji) was one of the Japanese guests. I don't know if this was been posted yet, but I thought I would give a summary of it. There were quite a few Detective Conan related questions (more than any other series other than Dragonball) which surprised me, but here is a summary of what he said:
Q: What do you think of Heiji's and Kazuha's relationship?
A: Pretty much Horikawa said that they do like each other, but he felt that "youthfulness" got in the way sometimes. In the end, he thinks they will get together.
Q: What is the difference between voicing Vegeta and Heiji?
A: Horikawa said that the characters are a part of him or that they come from within him ("jibun no naka") so he feels no difference between characters he voices. In particular, he emphasizes a part of his personality which matches with each character. Otherwise, he said voice acting would be quite difficult for him.
Q: Do you have trouble voicing Heiji's kansai-ben?
A: Horikawa is originally from Osaka, so he had no problems with that.
Q: Do you know who the leader of BO is?
A: Horikawa said that he does not know (no surprise!) and that the author is the only one who knows this information.
