With great concentration, you conjure up a gnoll disguise, allowing you to walk among the gnolls without interference. Listening to the little they speak of your language amongst themselves, you learn that they're raiding the main civilization in Westfall, compounding the refugees' problems. You intercept them at that raiding site by serving conjured military rations to the refugees, who help fight off the gnolls. It's so effective that the murderer personally approaches you, confessing to having committed the murder you were asked to solve, with the sole purpose of that confession being to help an attempt to hire you as a conjurer.
Hey, it's a job. Maybe you can make something great out of it. Report the murderer to the local authorities. Finish both sides of the equation.