In 2016, the number of homicides in Chicago jumped by 58 percent year over year. Why? Most social scientists have struggled to reach any firm conclusions. But in a speech on Tuesday in Gatlinburg, Tennessee, U.S. Attorney General Jeff Sessions claimed he’s found the smoking gun in a study by former federal judge Paul Cassell and economist Richard Fowles: It’s called the “ACLU effect.” Liberal police reform, this theory insinuates, is deadly business. Is Sessions right? Should we really be scared of the ACLU? No. The “ACLU effect” is a mirage.

Cassell and Fowles attribute the homicide spike to a drop in stop-and-frisk activity by the Chicago Police Department, which they tie, in turn, to a deal between Chicago and the ACLU requiring officers to document street stops more thoroughly. The agreement aimed to create a reservoir of evidence for determining whether stops are unjustified or discriminatory. The theory behind “the ACLU effect,” then, is that requiring officers to collect all this data slowed them down nearly to a halt. “If you want crime to go up,” Sessions scoffed, “let the ACLU run the police department.”

CPD’s street-stop activity did plummet by about 75 percent in late 2015—from around 40,000 stops per month to 10,000—as homicides and other gun crimes broke sharply upward. But that doesn’t mean the decline in street stops caused the homicide spike. For one thing, other crimes in Chicago didn’t jump nearly as much when stops slowed down. So Cassell and Fowles need some theory for why street stops, when conducted en masse, were depressing gun violence but not other crimes—such that, when stop and frisk dropped, gun crimes alone shot up. They don’t have one. In fact, other research suggests that when proactive policing slows down, we might, if anything, expect a greater increase in property crime than violent crime.

Second, why ignore all other cities? Street stops nosedived in New York just like in Chicago, yet homicides didn’t go up. Consider this as well: In either 2015 or 2016, homicides jumped as much in Austin, Texas; Memphis; Baltimore; Washington; Milwaukee; San Antonio; and San Jose, California, as in Chicago. Indeed, it’s not even clear that these spikes are atypical given historical homicide rates and fluctuations. In any event, if street stops hadn’t fallen before homicides spiked in these other cities—and I’ve seen no evidence that they had—this strongly suggests that other causes are at play.

There are other, better explanations for the decline in stop and frisk that have nothing to do with the ACLU agreement.

Likewise, Chicago homicides were already rising in 2015 before street stops declined. They had climbed 17 percent over the 2014 total, with the same or more killings in nine out of 12 months. Then homicides fell by 121 in 2017 (a trend that continues) while street stops remained (relatively) low. The point is that stop and frisk couldn’t have caused either of these changes—which occurred, respectively, before and after the ACLU agreement took effect—because stop and frisk itself was consistent during the pre–ACLU deal period and post–ACLU deal period. The study points out that CPD altered its tactics in 2017, rolling out data-driven command centers and gunshot detectors. If that explains 2017, though, then it would prove that we can fight crime without dragnet-style stop-and-frisk.

Third, a lot else was happening in Chicago during the period in question. CeaseFire, a well-regarded violence-prevention program, lost funding in March 2015. A study out of Northwestern University found that CeaseFire had reduced shootings by 41 to 73 percent in seven Chicago communities. And CeaseFire claims to have credible district-level evidence connecting the homicide spike to the program’s dismantlement.

The explosive Laquan McDonald video was then released in November 2015. Cassell and Fowles doubt the video mattered because, they say, the public knew about the shooting and cover-up months earlier. No Chicagoan who lived through the furor over the video’s release could possibly agree with the authors’ dismissive take. Cassell and Fowles also question why a video of police violence would trigger private violence. There could be any number of explanations. It seems quite possible, for example, that frayed ties between citizens and police affected how and when citizens called police and to what extent they cooperated with law enforcement officials.

There’s a second puzzle in all this: Even assuming the decline in street stops caused the homicide spike, why blame the ACLU for the decline in street stops? Stop-and-frisk activity actually began to fall in November 2015, six months before CPD finished preparing officers to collect data under the ACLU agreement. To state the obvious, the agreement couldn’t have caused a change in police activity that gathered steam before CPD implemented it.

Moreover, a parallel state law called SB 1304 took effect on Jan. 1, 2016, imposing new data-collection requirements on police throughout the state (including Chicago). The law and the ACLU agreement are not identical, but they’re similar. This means the “ACLU effect” is to blame only if the additional data-collection requirement of the agreement—just the increment that went beyond SB 1304—caused a massive decline in street stops. This is hard to believe.

There are other, better explanations for the decline in stop and frisk that have nothing to do with the ACLU agreement. In a climate of heightened scrutiny of police across the nation, release of the Laquan McDonald video put CPD under the microscope. In early December 2015, the U.S. Department of Justice opened an investigation of the department and Mayor Rahm Emanuel appointed the Police Accountability Task Force, which then released a critical, 190-page report in April 2016. At the very same time, CPD was rolling out body cameras, newly memorializing police encounters with an increasingly distrustful citizenry. Unsurprisingly, some research finds that officers who wear body cameras conduct fewer street stops. Again, none of this has anything to do with excessive paperwork. Instead, as CPD Superintendent Eddie Johnson put it, “no officer want[ed] to be on a viral video.”

Ultimately, the “ACLU effect” offers an alluringly simple explanation for the Chicago homicide spike, with national implications for crime control. The problem is it’s far too simple. And it needlessly sullies police reform’s good name.