Having spent much of the day reviewing disturbing documents, Jimmy was already in a bad mood, and Nia's call only worsened it.
Jimmy had seen his fair share of life and death, but those involved were criminals, mostly violent ones, so their deaths felt justified, lifting significant psychological burdens. Moreover, influenced by the remnants of the original Jimmy's soul, once he took action, he tended to do so with ruthless extermination.
However, after an exorcism by Priest Horton in Dallas, Texas, Jimmy managed to shed that occasional brutal state. Since then, his actions were relatively restrained, though he didn't hold back when necessary.
Jimmy had developed a considerable immunity to death around him, but for Nia, just a regular police officer who likely had never even fired a gun, including warning shots—judging from the usual experiences of most officers—this was different.