So even after Erich Ludendorff took the surrender of Liege, the forts surrounding the city held out against the invading Germans. That is, until the German Big Bertha arrived. The first ones had to be shipped by rail and assembled on site. Later, more portable versions were used. I think portable is relative, in this case. The shells, which were timed to explode after penetrating defenses, were so big that the act of firing them distorted the barrel. The more these howitzers were fired, the less accurate they were. Not that it really mattered. Once they were emplaced, they chewed through the fortresses in a matter of days.
As for Gerard Leman, he was found unconscious in the crater which used to be Fort Loncin and was taken prisoner.