NOPD Chief Michael Harrison went before the New Orleans City Council’s Criminal Justice Committee on Thursday to talk crime in the first few months of 2017. Per Harrison NOPD’s murder clearance rate is 31 percent so far in 2017 after clearing 41 percent of cases in 2016.

Clearance rates seem simple on the surface but they’re actually pretty complicated as Justin Fenton of the Baltimore Sun wrote earlier this month. The FBI considers a murder cleared when an arrest has been made or when the case has been cleared by ‘exceptional means’.

Clearing a case by exception requires that an agency has identified the offender, gathered enough evidence to make an arrest, identified the offender’s location, and encountered an issue that prevents arrest. This could mean that the offender is dead (think a murder-suicide) or the offender is in jail in another city for another murder.

It’s important to note that murders cleared by warrant do not count in the eyes of the FBI.

With the definition of a murder clearance established it’s worthwhile to dig into how they are calculated from year to year. A current year’s murder clearance rate is gathered by dividing the number of murder clearances obtained in a given year by the number of murders for that year. And that’s where the complexity lies.

Consider a city that had 10 murders in 2015, 10 murders in 2016 and 20 murders for the first four months of 2017. Now let’s say that city solves none of the murders in 2015 and 2016 but then in 2017 arrests a serial killer for all of the 2015 and 2016 murders. That city will have solved 100% of the previous two year’s murders but will claim a 0% clearance rate for those two years while also claiming a 100% clearance rate for 2017 despite having solved none of those crimes.

Rather than telling us how many of that year’s murders the homicide unit is clearing the murder clearance rate gives a distorted look at a general confusing trend.

With that in mind let’s turn to the claims of 41 percent clearance in 2016 and 31 percent in 2017. There were 174 murders in New Orleans in 2016 and 61 so far in 2017.

Breaking down those murders paints a much clearer picture of how many murders of each year’s are being solved in New Orleans. Let’s start with 2017.

There have been 61 murders so far in 2017 and NOPD has made an arrest in 11 of them. In a logical sense that would make NOPD’s murder clearance rate 18% for the year. So how did NOPD reach the 31 percent clearance rate?

There were “only” 51 murders in New Orleans as of the end of March when NOPD calculated the statistics presented to the council. Of those 51 NOPD had made arrests in 10 of them by the end of the first quarter according to Matt Sledge’s 2017 murder spreadsheet. That’s good for 19.6 percent of 2017 murders cleared as of the end of March.

The 31 percent of 51 murders must mean that NOPD solved 6 old murders in 2017, and a quick chat with New Orleans murder tracking guru Muspench confirms that there have been six arrests made of 2016 murders so far in 2017. A review of NOPD’s homicide spreadsheet (obtained through a public records request) shows that half of those six arrests were cleared by warrant in November 2016 with the arrests occurring in early 2017 while the other three arrests were open cases as of the start of this year.

Next let’s turn to the city’s 174 murders in 2016. NOPD claimed a 41 percent clearance rate for 2016 which means either 71 or 72 murders clearances were obtained in 2016. A review of the official homicide spreadsheet shows 46 of 2016 murders were cleared in 2016 meaning 25 or 26 of 2016’s murder clearance rate is old murders solved last year. Adding in the six 2016 murders cleared in 2017 brings the total to 52 of that year’s 174 murders have been cleared so far.

The below table breaks down how NOPD reached clearance rates of 31 and 41 percent for 2017 and 2016 as well as the actual percent of each year’s murders being cleared.

Clearance TableIt’s not NOPD’s fault that the way the FBI tells them to count murder clearances makes the figures distorted and complicated to follow. The department’s terrific transparency and local media sources make it possible to figure out how these numbers are calculated and how 18 percent in reality can turn into 31 percent officially.