Work on the Zweilicht had been going on for many a year prior to you meeting the good doctor, Mr. Blackwell. Reinhardt saw the signs, he was right in guessing that Second Impact had damaged Ahriman's seal sufficiently to begin letting fragments of the demon's Id spill into this world.

And I'd met him many times... but always in different locations. Like... he'd work on something somewhere, only to drop it and move halfway across the planet before resuming.

I think he was being followed. Or under observation from people or things he didn't want to be. And whenever he'd change locations, he'd leave behind everything he could, including weapons he'd designed for the Zweilicht. Maybe he intended to go back for them some day; though obviously he won't be now.