Thomas attacks them bodily to try and buy himself sometime to disconnect them properly, but a second group appears to interrupt his attempts. In dealing with the second group and trying to keep the first down, a piece of debris gets driven by wind and momentum across the scene and cuts through the physical piece of his line, disrupting the circle that keeps the magic held tight within.
Using the greater awareness he's been having over the weave of magic in the area, he tries to focus past the sounds of fighting and gunfire in order to perform a sealing ritual similar to what he put around the building but in a smaller area, trying to catch all the golems within so that they'd be disconnected from whatever was driving them. To give himself a great chance, he uses the larger crystal and a heart he managed to grab from one of the golems in order to perform a bit of sympathetic magic. In great pain and desperation, he manages to pull it off with a spectacular bit of magic that impresses all involved while disrupting the golems and causing them to fall inert.