Gang violence is nothing new, but it’s a problem that has grown significantly out of control. There were 2,363 gang-related killings in the United States in 2012 — the highest number in six years, according to estimates from the Department of Justice.

In an effort to understand how this violence crops up in certain places, researchers from Michigan State University (MSU) took a look at the patterns in which gang slayings occur. The groundbreaking findings, published in the American Journal of Public Health, detail how gang violence generally moves in a consistent pattern over time, not unlike infectious disease. These violent crimes seem to move from one vulnerable area to the next.

"We've shown that there is a potentially systematic movement of gang-related homicides," lead study investigator April Zeoli, an associate professor of criminal justice at MSU, said in a press release. "Not only that, but in the places gang homicides move into, we see other types of homicide; specifically, revenge and drug-related killings — also clustering.”

Zeoli added that together, these findings allow for experts to better predict where gang homicides will be the most concentrated. One possible precedent of violence could be changes in gang networks.

In 2012, Zeoli and colleagues Sue Grady, Jesenia Pizzaro, and Chris Melde showed for the first time that homicide "spreads like infectious disease." Similar to the flu, homicide needs a susceptible population, an infectious agent, and a vector to spread efficiently. As far as gangs are concerned, the infectious agent could be, for example, a street code — guarding one’s pride at all costs. The vector, on the other hand, could be word of mouth or publicity, Zeoli said.

The study utilized police data from Newark, N.J., and included information on not only homicide, but robbery, revenge, drugs, and domestic violence. Researchers found that gang homicides occured in patterns, and that the type of homicide can have an effect on the pattern. The homicides that stemmed from domestic violence and robberies, for example, did not show signs of spreading or clustering.

Revenge and drug-related homicides did seem to cluster, and they clustered in the same areas as the gang murders.

"By tracking how homicide types diffuse through communities and which places have ongoing or emerging homicide problems by type, we can better inform the deployment of prevention and intervention efforts," the study says.

Source: Zeoli A, Pizarro J, Melde C, Grady S. “Modeling the Movement of Homicide by Type to Inform Public Health Prevention Efforts.” American Journal of Public Health. 2015.