How Many Uncaptured Serial Killers Are Out There?

> The rate for cleared homicide cases is "the lowest in the Western world," Hargrove said. > Other reasons may also explain the low rate of arrests, including a high bar for making an arrest as well as what some call an increasing no-snitch culture, especially among some minority groups who are reluctant to come forward as witnesses, according to experts interviewed by NPR. The US is kind of a big place compared to the rest of the Western world. Also the mention of "no snitch culture" would indicate gang violence. Do they consider "hit men" to be serial killers?