When the thing was getting ready to explode, Heisenberg had no idea what to do as the thing went out of control. That was pretty much the end of any serious German work towards a nuclear weapon.
Let me add my vote to that excellent and very entertaining book.
Expedition Wild (Josh Gates) had one show where they were exploring buried Nazi caves. They had to back out when their Geiger counter had a really high reading.
Calling that a “nuclear accident” is a slight stretch IMHO; the accident (as I read it in the Wikipedia article you provided) had nothing to do with a nuclear reaction; it was a result of the pyrophoric nature of powdered uranium; all the heat energy that powered the steam explosion was provided by chemical processes, unlike (say) TMI, Fukushima or Chernobyl.
Anyway, still an interesting story. It sounds like Heisenburg and his co-workers didn’t really put their hearts into the effort, which would have caused (I imagine) very serious consequences for them if der Fuhrer had known about their real feelings.
Still, it’s obvious in hindsight that they could never have made it, particularly before the end of the war. They had no way of separating the U-235 isotope, which even if they had known how to do it would have required industrial resources that Germany couldn’t spare at the time.