“A lot of the stuff from the street sort  of spilled into the diner,” Papachristos said. “Whether it was the politicians, the gang members, or the cops, all of that  was playing out in front of me.”

Papachristos said he followed his interest in crime and came to criminology and sociology “late” in his college career as a junior in college. After graduating, Papachristos actually had an offer to become a police officer.

As the son of Greek immigrants and a first-generation college student, it made sense to get a practical job, and being a police officer aligned with his interests at the time. “My parents didn’t know anything about college, but they knew they wanted to send their kids to college,” he said. “So, what do you do after college? You get a job.”

But instead of becoming a cop, Papachristos got into a master’s program at the University of Chicago and worked a few years before going back for his doctorate in 2001. Papachristos is now studying how network science–the study of how social relationships affect what people feel, think, and do–can be used to understand the spread of crime and gun violence.

After 10 years away from Chicago working at the University of  Massachusetts Amherst and Yale University, Papachristos is moving home to join Northwestern and the Institute for Policy Research to continue his work on network science and crime.

Understanding Gun Violence as an Epidemic

According to Papachristos, gun violence is a lot like an epidemic: It concentrates within networks of people, it transmits from person to person, and it’s socially “contagious.”

In other words, if a person is around someone who has been exposed to gun violence, he or she is at a higher risk of becoming a victim, too. In one study, Papachristos and his co-authors found that almost 90 percent of shootings were within a single, large network made up of just 6 percent of the city’s population.

Papachristos pointed to the shooting death of a 6-month-old girl in 2013 as an example. In the three years prior to the girl’s death, her father, the intended target, was arrested 23 times with 17 different people. Of those 17 people, 40 percent were shot.

Papachristos said though shootings may seem random, whom someone is with at a given time can increase his or her risk of being shot. “You can be pulled into a dispute just because you’re at a party as a plus-one,” he said.

So How Do We Treat the Epidemic?

Papachristos said communities need to reach out to the right people in the community to help reduce trauma and retaliation immediately after an incident-not just law enforcement, but also educators, outreach workers, public health professionals, and service providers.

“I’m talking about trauma care specialists, violence interrupters, outreach workers, case managers, priests, football coaches, teachers-everybody we need, we can direct them in this network context,” Papachristos said.

He added that cities also need to address the issues that create these networks in the first place, like poverty, segregation, over-policing, and struggling schools. “We need to work on the big stuff at the same time,” Papachristos said.

In Chicago, A Gun Just “2.5 Handshakes” Away

Papachristos is also examining how guns move throughout these networks. He is the senior author of a new study that found that in a network of 188,000 people arrested in Chicago, any individual was just “2.5 handshakes” away from a gun. “If you’re in a gang, you’re about 20 percent closer,” he added.

According to Papachristos, most people don’t regularly carry guns, but only do so when there is a perceived need to protect oneself. “It doesn’t matter if you’re on the South Side of Chicago or in rural Louisiana, the idea that guns afford protection
is deep-seated in the American psyche,” Papachristos said. But in addition to the demand for guns in Chicago, there’s an important supply-side, he said.

“It’s really easy to go not so far to get a gun in Chicago,” Papachristos said, noting the proximity of suburban gun shops, and nearby Indiana, which has fewer gun control laws than Illinois.

Is Police Violence Also Contagious?

In a forthcoming study, Papachristos and his colleague, Daria Roithmayr from the University of Southern California, are examining whether or not police violence is also contagious.

They are examining police complaint data from the Invisible Institute to see if there are social connections between officers based on complaints people file against them. “It’s more than just ‘bad apples,'” Papachristos said.

Police  officers learn certain bad behaviors–like violence against suspects, turning off body cameras, or lying on official reports–from each other. While the research is still ongoing, Papachristos said they are starting to see patterns of multiple complaints within the same networks, like excessive force.

Identifying the Network

“As with the discussion about gun violence, if there’s a network and we can identify it, we can also use that information to do something about it.” Papachristos is now bringing this kind of work to IPR, where he will once again get to work in the city he so often studies.

He said he is excited about working with professors from other disciplines. “True interdisciplinary work is rare,” Papachristos said. “That’s where good work happens.” He is also launching the Northwestern Neighborhood Network nitiative, where he plans to promote creative research projects to leverage the idea that networks matter in improving cities.

“I’m ready for the next step,” he said. “I’m ready to come home.”