Some questions to consider
This is a neat situation...there's a lot of different ways it could play out.
This Ishimura--you couldn't find out anything about him, right? And that's with a pretty impressive effort (Gather Information 45). So he's either a new threat, or a old threat using a new name. If he's a new threat, he didn't accumulate his power overnight, so he has to have come from somewhere else. Do your characters have any major contacts outside the city? Could he be tied to the Japanese Yakuza (who see an opportunity to move on Montreal now that a 'soft' leader has been given control over the local mafia)?
If he's an old threat with a new name, do his methods ring a bell with any of you? Any villians tried this sort of scheme with you before? Don't forget about any foes you may have thought were dead--tricky DMs have a way of using them against you.
Oh, and have you tried to translate Ishimura's name? Maybe there's a clue there, maybe not.
What about the mole that Lawson said he caught? Any info there, or is it really a dead end? And where did this armor come from, anyway? Is Lawson really developing it, or is it something he found and is trying to replicate? That would explain why it's too valuable to lend to you--it might actually be one-of-a-kind, irreplaceable. Could Ishimura actually just be trying to recover something stolen from him? The armor sounds like magic--could it be?
This is really out on a limb here, but could your new employee (Tim) be involved in this? I mean, if he's an expert Inflitrator, could he be infiltrating you? Of course, maybe your DM doesn't go in for really evil tricks like that, but it's worth considering.
I don't trust Lawson, but I'm don't think he's involved (or secretly a cover for) this Ishimura character. I just can't see where the advantage would be for him. Still it was awfully cold of him to suggest that you just let your secretary get killed...feels like there's something suspicious there, but I just can't put my finger on it.
Anyway, I hope that perhaps some part of my random musings may be of help to you. Let us know how things turn out, okay?