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How We Reported on Rising Gun Possession Arrests

The Marshall Project used arrest data in Chicago and other cities to understand who was arrested for gun possession and how the number of arrests changed over time.

The Marshall Project found that in Chicago, arrests for gun possession are rising and police are overwhelmingly arresting Black men. At the same time, gun violence continues to kill or injure Chicagoans, while few victims see arrests or other closure in their cases.

To report this story, we:

We obtained records of arrests that would include gun possession from public records requests

The Marshall Project filed public records requests for records of arrests where the person arrested was in possession of a firearm, along with records of associated charges and firearms recovered.

We requested all charges related to the arrests in order to see which crimes were charged in the arrest in addition to gun possession. For example, some arrests may start with a traffic violation, but also include a gun charge when looking at all charges.

Requesting charges as a separate table of data also avoided potential errors in counting arrests that could occur when working with pre-joined data rather than joining the data ourselves. We used the Central Booking (CB) number, which uniquely identifies an arrest report, to join the arrests with other data sets.

We requested all arrests in incidents that involved a gun because we wanted to have flexibility in how we defined gun possession arrests, and also understand the quantity of gun possession arrests relative to other kinds of gun crimes. Arrests where gun possession was the most serious charge made up the majority of arrests in the response, and a growing share over the data's 13-year time period.

We needed more information than what is available in public data

The arrest records we obtained are similar to the arrest data published on Chicago's data portal. However, in addition to only reflecting arrests involving guns, there are some other key differences. The data we used:

Both the public data and the data we received in response to our records requests exclude arrests of people under 18.

We identified arrests where gun possession was the most serious charge

There are multiple crimes that could fall under the category of gun possession. We had to decide which ones we wanted to include in our definition, and make a way to filter the arrest data to records that reflected those crimes.

Our reporting focused only on arrests for gun possession — not arrests where someone was charged with firing a gun or using one when committing a crime such as robbery. We also wanted to exclude arrests for crimes like selling guns.

We reviewed statutes in the charge data and the text of the state and municipal laws to select the ones which covered illegal gun possession. We compared the selected statutes with ones included in the analysis for a 2022 report on illegal gun carrying arrests by the Illinois Criminal Justice Information Authority (ICJIA). The possession statutes we used are consistent with the ones identified by the ICJIA researchers. However, the ICJIA researchers also included statutes that cover crimes related to the use of weapons in other crimes, such as “Armed robbery, aggravated vehicle hijacking with a firearm” (720 ILCS 5.0/18).

The researchers' analysis also included statute sections that can cover both the possession and discharge of guns. We used more narrow filters to only flag charges that match statutes that deal with possession.

Finally, the ICJIA analysis, which looked at arrests statewide, considers only state laws. Since most of our analysis is focused on Chicago, we also included a few charges for violations of the Municipal Code of Chicago.

We used Python code to parse the statutes to make them easier to match and flagged each charge where the statute was for gun possession. This code also compared the charges within an arrest and flagged whether a particular charge had the highest type and class. Finally, these flags were joined into the arrest data. This allowed filtering arrests to ones where a gun possession charge was among the most serious charges. We used this subset of the original gun arrest records when calculating statistics about gun possession arrests.

We analyzed the gun possession arrests to see who was arrested and how the number of arrests changed over time

We aggregated the arrests where gun possession was the most serious charge in a variety of ways to better understand the dynamics of gun possession arrests.

We looked at the gun possession arrests over different time periods, by race and ethnicity, by age, by sex, by community area and by block-level address.

To understand how the race and ethnicity of those arrested for gun possession compared with residents of Chicago, we used five-year estimates from the U.S. Census Bureau's 2020 American Community Survey (ACS). This allowed us to use a consistent source with community-area tabulations of the ACS data made by the Chicago Metropolitan Agency for Planning.

Arrest data, as well as other data sets produced by the Chicago Police Department, include racial categories of “BLACK HISPANIC” and “WHITE HISPANIC” in addition to “BLACK” and “WHITE”. For analysis, the “BLACK HISPANIC” and “WHITE HISPANIC” categories were re-coded to a separate category for any Hispanic person arrested, similar to how many analyses of data from the U.S. Census Bureau analyze counts of Hispanic or Latino people of any race alongside counts of non-Hispanic people by race.

The field reflecting the sex of the person arrested is labeled “SEX” in the source data. While the Chicago Police Department has issued directives for interactions with transgender, intersex and gender-nonconforming people, the source data only included records with codes indicating the person arrested was male, female or in a very small number of cases, their gender was unknown or they did not provide their gender to police.

We compared the demographics of people whom police arrested for gun possession with the demographics of everyone police arrested and the overall population. For the demographics of all people police arrested, we first used the public arrest data and later used aggregates of adult arrests by race obtained through a public records request.

We built a database of arrest reports from two holiday weekends

In addition to analyzing the gun possession arrest data, we also wanted to understand some of the dynamics that aren't reflected in the data: what led to the initial police stop, how police conducted the arrest, and what information the police knew about the person arrested. To help understand this, we used the arrest data to retrieve arrest reports, either from public records requests or viewing them at a Cook County courthouse. Viewing records at the courthouse allowed us to access hundreds of arrest reports at once and avoid potential redactions.

We selected arrests for the 2022 Memorial Day and Labor Day holiday weekends. Gun violence in Chicago peaks in warmer months, and media and officials often use these weekends to contextualize violence and policing.

The Marshall Project read hundreds of arrest reports and built a database to capture properties of the arrest. Each report was read by a reporter who entered the arrests’ properties into the database, as well as a second reporter who checked the entry. In cases where the correct categorization of an arrest was ambiguous, the reporters conferred and occasionally consulted other reporters in the newsroom to make a final decision.

While reading the arrest narratives gave reporters a better sense of how police arrest people carrying guns, we also did some quantitative analysis of the hand-built database. Before analyzing the records, we limited them to arrests that fit these criteria: They were in the most recent version of arrest data, they occurred from 5 p.m. on Friday through just before midnight on Monday, and the police did not make an arrest in response to a reported or observed safety threat.

We then calculated statistics about the percentage of arrests that started with a traffic stop; where officers said they smelled marijuana; where the person arrested had a FOID card, but not a CCL; where the person arrested had an outstanding warrant, were on parole or probation, or police reported the person had some gang affiliation.

Beyond these efforts, we also filed public records requests for body camera footage to gain even more insight into the policing culture involved in gun seizures.

We followed many connections, including ones from data, to speak with people who were arrested

The core part of our story focuses on the people directly affected by this type of policing. In order to find men and women with lived experiences, we relied on community organizations, academics, public defenders, and advocates to connect us to potential sources.

We also conducted group interviews with men most at-risk of being a victim or perpetrator of gun violence in Chicago, so we could better understand the street-level culture around illegal guns. We also read through state appellate court rulings to gain insight into how the methods that police use to find these firearms stand up in court.

Additionally, we wrote letters to people incarcerated for nonviolent gun crimes as well as those navigating active gun cases. Separately, we used the arrest data we obtained to “cold call” dozens of people to learn about their case and experiences with the legal system.

We obtained records for victims of fatal and non-fatal shootings to calculate whether there was an arrest in a case

We wanted to understand gun violence trends in relation to gun possession arrests. To do this, we obtained data about non-fatal and fatal shooting victims from 2010 through 2022 using public records requests. The data we received is similar to victim data available on the city data portal. Critically, the data we received also includes fields that indicate the victim's case status or whether a victim's case was cleared (and whether it was cleared exceptionally). Along with the data on victims, we also obtained records of arrests related to the victims’ cases.

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We used the shooting victims’ data to look at how the number of victims changed over time and relative to gun possession arrests. We plotted this relationship at the community area level to see which neighborhoods had outsized increases in gun violence, and arrests in recent years. We also looked at gun violence victimization and possession arrests within neighborhoods over time to contextualize recent trends.

From our analysis of the possession arrest data, we knew that police had increased gun possession arrests over the time period of our data. We also wanted to know how arrests in shooting victims’ cases had changed over the same period. Sources from our reporting told us that holding shooters accountable was extremely important to communities that faced high levels of gun violence, but that investigating shootings used very different policing resources than the kinds of stops that result in gun possession arrests.

To determine the percentage of victims where police made an arrest in their case, we used a conservative measure: whether either the status fields in the record for a victim's case indicated that police had cleared the case through arrest, or if an arrest could be matched with the victim's incident through the RD number. We also checked that, even when considering cases police cleared without making an arrest, the data showed that the vast majority of victims did not have their case cleared, nor did police make a related arrest.

We used numbers from annual reports to understand long-term trends in arrests

While we analyzed arrest-level data from 2010 onward, we also wanted to see the longer-term trends in gun possession arrests. We were able to find aggregate statistics for weapons arrests, a category that includes, but is not limited to, gun possession, from police department annual reports going back to 1965.

The statistics were entered by one reporter and checked by another. When a statistic for a particular year appeared in multiple reports, the most recent report’s number was used.

While the annual report data did provide some insight into long-term arrest trends, the data was limited by missing reports, missing demographic breakdowns, changing racial categories and how Hispanic arrestees were reported. We were able to visualize a count of arrests of Black people because this racial category was consistently defined across the years of reports.

We also inspected data from the FBI's Uniform Crime Reporting program to look at long term trends in Chicago weapons arrests. However, this data also had issues with years when the department did not report data.

We also compared aggregates we calculated from individual-level data with the numbers published in the annual reports.

We also examined weapons arrests data from other cities

Even as the reporting focused on Chicago, we still wanted to look at how arrests for charges that include gun possession were changing over time in other cities. We also wanted to see whether Black people made up the vast majority of those whom police arrested, as they did in Chicago.

We processed and analyzed weapons arrest data from a few cities that shared some properties with Chicago, but differed in others when considering population, region of the country, permissiveness of state gun laws and percentage of Black population. We examined data from Cleveland, Ohio; Houston, Texas and New York, New York.

We tried to filter the arrest records to include only arrests where the charges reflected gun possession. However, the statute fields did not always have enough specificity to differentiate when laws governed both guns and other weapons. In these situations, we included the arrests. Unlike the Chicago data, the arrest data from other cities did not include all charges associated with an arrest, so we were not able to know how many of the weapons arrests also included charges where a gun was used in some way.

We read widely to inform our reporting

We consumed as much media about this issue as we could, and in addition to our other reporting channels, relied on books, law reviews and research to understand gun enforcement history and policy. Here are some we found notable:




Geoff Hing Twitter Email is a data reporter for The Marshall Project. He has worked as part of investigative, data and news applications teams in a number of newsrooms. At The Arizona Republic, Geoff covered demographic change in the state and contributed data reporting to enterprise projects on water use and prison labor. At APM Reports, he covered voting rights and analyzed police use-of-force data and records as part of a team investigating the efficacy of Tasers. And while at The Chicago Tribune, Geoff helped analyze and visualize police accountability and shooting data.

Lakeidra Chavis Twitter Email is a staff writer for The Marshall Project. She has written extensively on gun violence and gun enforcement in Chicago, as well as Black suicides, gang structures and the opioid crisis. Her work currently focuses on juvenile justice. She previously reported at ProPublica Illinois and for NPR stations in Chicago and Alaska. Lakeidra was a 2021 Livingston Award finalist. She lives in Chicago, Illinois.