Chicago has one of the highest homicide rates in the country and one of the worst records for solving murders. And while a lot has been done to address the root of the violence, far less attention has been paid to just how many of these murders do — or don’t — get solved.

A few years ago, Mikki Kendall, a well-known feminist author, began noticing a pattern in dead bodies that were dumped on the South Side — women who were stripped naked, stuffed in dumpsters and burned. In 2007, two women were found strangled in burning dumpsters near Washington Park. And an investigation by VICE News found four more instances of women who died in the same way over a ten year period.

None of these murders were ever solved.

Tom Hargrove, an investigative journalist and the co-founder of the Murder Accountability Project, also noticed that a disproportionate number of women were being strangled in Chicago. In 2015, Hargrove and his partner, a retired homicide detective and FBI agent, developed an algorithm that detected patterns in murders across the country. That algorithm, according to Hargrove, was sounding “red alert” that there was a serial killer operating in Chicago.