Harold Pollack cares deeply about Chicago’s murder problem and he knows a lot about it too. In 2008, when he was part of the team working to establish the Crime Lab at the University of Chicago, he read through medical examiner reports for 200 consecutive homicides of young men in Chicago, and a couple things about the murders really stood out.

“They were impulsive acts where a gun was present, and so an altercation that would have led to somebody getting punched in the face suddenly becomes someone being sent to the morgue,” said Pollack.

Another thing that stood out to him was just how deadly guns can be, and like all of us who grieve over the high number of young people being killed, Pollack is looking for any solutions that could help reduce the number of murders in Chicago.

“We have many people in the city walking around carrying these really lethal weapons and causing tragedies for themselves and other people and if we can make that less common by the imposition of the risk that they’ll face some sort of a mandatory minimum sentence if they’re caught, I think we’ll save some lives,” said Pollack.

That’s why Pollack supports Mayor Rahm Emanuel’s push to impose mandatory minimum 3-year sentences on all people caught carrying an illegal gun. In fact Pollack testified in Springfield before legislators considering the law, and his appearance carries some weight because he’s the co-director of the Crime Lab at the University of Chicago, which is dedicated to using science to improve crime policy. So as I was doing research for this story I went to Pollack to see what research he has to show that mandatory minimums will work. His answer surprised me.

“Well I don’t think we have research that nails it down,” said Pollack. “I must say I personally am very influenced by the situation in New York.”

The situation in New York — that’s one of the main “arguments” Emanuel and Chicago Police Superintendent Garry McCarthy have repeatedly made over the past few months as they’ve pushed their agenda on gun legislation..

“And just look at New York,” said McCarthy at a press conference this week. “It couldn’t be a clearer example of how to do this. The fact is, where these conditions exist, it’s working. I mean, what research do we need?”

Well, Frank Zimring did do the research. He’s a professor of law at the University of California Berkeley and author of the book “The City That Became Safe: New York’s Lessons for Urban Crime and its Control.”

“The mandatory minimum punishments, is, if you study the New York experience, beside the point,” said Zimring.

Zimring studied 19 years of data tracking crime in New York. He says in 1990 the city had 2,250 murders. In 2012, it had 419. That’s an astonishing 80 percent drop in murder.

It’s that success that’s being used to justify the mandatory minimum sentences being proposed by Emanuel and McCarthy, but mandatory minimums weren’t signed into law in New York until late 2006.

“That’s after 90 percent of the crime reduction!” said Zimring. “I think that what’s going on is that the superintendent and the mayor in Chicago are under a ‘do something fast political pressure,’ and in my experience, at least, that’s never been good for penal codes.”

So, mandatory minimums were not part of the formula that led to New York’s success. But can they work to deter crime? Police Superintendent McCarthy has been making the argument that they can.

At his weekly press conferences on guns and mandatory minimums McCarthy has been profiling cases where young men who had previous gun charges are either shot or charged with shooting someone. Here’s what he said at a press conference at the beginning of April:

“Akeem Manago was shot and killed this weekend. In April, less than a year ago, 2012, he was sentenced to 42 months for aggravated battery and one year for aggravated UUW.  He was paroled on January 28th and two months later he was shot and killed. With truth in sentencing he would have been incarcerated instead of on the street to be a crime victim,” said McCarthy.

“It’s an emotionally powerful claim your police chief is making,” said Mike Tonry, a professor of law at the University of Minnesota. “Probably most people’s intuition is that it’s legitimate, which is why it’s an effective public argument. Of course it’s completely intellectually dishonest.”

“It’s simple, with 100 percent  accuracy, to make statements like that retrospectively, say, this guy was convicted, didn’t go to prison, six months later committed an offense, don’t you see if he had been sent to prison six months ago this wouldn’t have happened,” said Tonry. But he says the problem is that if you go back six months and look at the number of people who came to the attention of police that day, there’s no way to know which ones would reoffend in the future unless you lock them all up and that gets costly.

The Illinois Sentencing and Policy Advisory Council has studied Emanuel’s mandatory minimum and told legislators that if the law had been in effect over the last three years it would have cost the state an extra $400 million in incarceration expenses.

Tonry says there are better ways to spend that money to bring down crime. “You could do some things with greater police intensity, changes in patrolling techniques, all kinds of outreach work with gangs, all kinds of community center stuff that would probably be more effective,” said Tonry.

In a 2009 paper on mandatory minimums Tonry looked at sentences before the laws took effect and after and surprisingly he found that the sentences were often exactly the same. The mandatory minimums had no effect because prosecutors and judges simply found ways to work around them, most commonly by bringing charges without attached mandatory sentences.

In such cases Tonry says the mandatory minimum laws are just political theater and fall into a category of law called expressive punishment laws.

He explains them as “Laws that are meant to essentially convey a message to the public irrespective of what they do in practice, and since your mayor is a smart guy and I’m sure he is surrounded by smart people, I have no doubt that they perfectly well understand that this is a symbolic proposal of their making and if it’s enacted they will claim credit for having responded to public anxiety and having done something about whether or not it’s likely to have any effects in the real world,” said Tonry.

But so what?  What’s wrong with passing a law that says we as a state take it very seriously when people carry guns illegally?

Tonry says if the mandatory minimum proves misguided as such laws often have — it will be  tough to take back. “No state has yet repealed any major bit of expressive tough-on-crime legislation,” said Tonry. “It’s really hard to do.”

Emanuel has said he’s confident that mandatory minimums will be part of any new state gun legislation. In announcing his push for mandatory minimums he said, “When you commit a serious gun offense, you should serve the time. The victims deserve it, the public demands it, and the criminal justice system shoud deliver it.”