This has to do something about DC OVA 6. During that time as I was watching the OVA, the criminal sounded just like Hattori Heiji. But, I finally got to handle the DIFFERENCES BETWEEN HATTORI AND HIS IMPOSTOR. Here are the clues:
1. Doesn't use the standard Japanese accent. As what I have said, Hattori uses the Kansai-ben language but, his impostor uses the standard Japanese accent.
2. Calls Conan, "Kudo". Usually, Conan picks up the Detective Agency's phone. Whenever he says, "Hello?", Hattori always (or sometimes) says, "Ah! Kudo" but his impostor didn't recognized Conan.
3. The subtitles. Heheh. This is VERY EASY to notice, right? You see, if a person who uses the standard Japanese accent , the subtitles are ALWAYS (or maybe not) the standard English language. BUT, if it were a Kansai-ben user, here are the change of some words/phrases:
you = ya
your = ya or yer
my = (not usually used) mah
"What do you?" = "Whaddya mean?"
"What are you?" = "What'cha? or What are ya?"
For short, uses the "somewhat-like" Cowboy accent.

I swear that ya won't be fooled. Ja, kiyotsukete yo, minna! Ja mata!