Hadley took the forced transfer personally, and began to target Peter Mills and Kelly Severide, his former lieutenant. Hadley started fires at particularly difficult buildings that were listed on the "dangerous buildings" list.

Did Hadley start the fires in Chicago fire?

Hadley played a prank on Mills, putting dog food in his meal, and that resulted in Chief Boden forcibly transferring him out of 51. That set Hadley off and set him on a rampage as an arsonist. He started fires in structurally unsafe buildings and targeted Severide and Mills specifically.

Is Hadley the arsonist on Chicago fire?

Kevin Hadley was eventually arrested and found guilty of arson. He is currently serving his sentence in prison.