If I asked you to think of a murderer, what's the image that springs to mind? If you're like most people, you'll probably think of an evil psychopath, or someone bent on revenge. Perhaps you'll see a criminal mastermind, who eliminates rivals on his way to riches. Or a strung-out drug addict, who kills because she needs money to get high. All of these images have something in common: As a rule, we tend to associate murder with the behavior of individuals who behave in aberrational ways.
"We think of individuals who commit homicide as being unlike the rest of us," said April Zeoli, a public health researcher at Michigan State University's School of Criminal Justice. "They are crazy, or substance users, or had a bad childhood. There is some reason specific to the individual that they are committing homicide."
Zeoli recently decided to test that theory using the lens of public health research: When scientists study the outbreak of an infectious disease like AIDS or the flu, they don't ask what it is about specific individuals that made them sick. They look for broader patterns, knowing that illness in any individual stems from a process of contagion.