If you kill the Crooked Man at the foundry, Bigby will brutally choke him to death in the foundry.
Bigby then returns to the Business Office (with the same people listed above waiting for him) with the Crooked Man's corpse, and the scene (compared to if you return with him alive) is drastically different; the community is very skeptical about the acceptability of Bigby's actions. As Bigby's hearing progresses, he (alternative to deciding the handcuffed Crooked Man's punishment) will have the choice of either leaving the area.
If he leaves, then Bigby will berate the community for criticizing him for the effort he went through to kill the Crooked Man as he throws his corpse down the witching well and walks away.
If he stays, Nerissa comes in and explains how she and the other girls were prisoners at Georgie's club, and that it was the Crooked Man who coerced Georgie into ordering their deaths. As their names are cleared in front of the community, Bigby and Snow are accepted as the revolutionized Fabletown government, and the Crooked Man's corpse is thrown down the Witching Well.