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What is a gang, anyway?

That’s one of many questions raised by the huge amounts of data collected and maintained by the Chicago Police Department.

As I wrote in a column this week, nearly 129,000 people are identified as gang members in what’s commonly known as the department’s “gang database.” The gang data is marred by inconsistencies and mistakes — 13 people in it are listed as 118 years old, for instance, and two others are supposedly 132. The errors can lead to lives being upended by incarceration and deportation.

“It’s really affecting people in a lot of different ways, and in ways we don’t even know because we don’t know how this information is shared,” said Vanessa del Valle, a clinical assistant law professor at Northwestern University law school’s MacArthur Justice Center.

Consider this: Two of the people in the police database are listed as members of the Black Panthers — the black power organization founded in the 1960s.

According to the police records I acquired, one of the Panthers in the database is now 64 years old and was arrested in 1987. The other, 38, was arrested in 2003. The records don’t show why either was picked up.

But the fact they were labeled as Panthers in the database is potentially problematic.

The Panthers were controversial from the beginning, and for five decades, some law enforcement officials have viewed them as a gang or band of insurrectionists rather than a political organization. During the 1960s and ’70s, the FBI led a well-documented and ugly campaign to undermine the group.

As recently as 2015, the Police Department opened an investigation to monitor current members of the Black Panther Party after they participated in Black Lives Matter protests.

This is just one example why many civil rights advocates are wary of the gang database.

“For me, it is important to come back to this broader question about surveillance and data,” said Andy Clarno, the coordinator of a research group at the University of Illinois-Chicago that issued a February report on the gang database.

“When there’s a justification granted to the practice to look at one group of people, it legitimizes the practice so it can be used much more broadly.”

After I started asking police about the database this week, they said they were working on changes that would let people correct information about themselves and be removed from the list.

I hope you will read this week’s column, my latest look at politics and policy in Illinois. And if you have any thoughts or tips about the gang database or other issues in your community, please drop me a line at mick.dumke@propublica.org.