Stranger murders are particularly difficult cases to clear; here I'm talking about "real felonies" in general, and I'm also speaking very generally. E.g. Chica

Stranger murders are particularly difficult cases to clear; here I'm talking about "real felonies" in general, and I'm also speaking very generally. E.g. Chicago's murder clearance rate for 2016 murders has plummeted to 21% (http://www.chicagotribune.com/news/local/breaking/ct-chicago-homicide-clearance-rate-20160909-story.html http://www.chicagotribune.com/news/local/breaking/ct-chicago...). Here in my above average crime rate (old mining town) corner of SW Missouri, the murder clearance rate is very high. However, the first relevant thing I found on Google was a State Police summary document for 2013 (https://www.mshp.dps.missouri.gov/MSHPWeb/SAC/pdf/Crime%20in%20Missouri%202013%20ver%205.pdf https://www.mshp.dps.missouri.gov/MSHPWeb/SAC/pdf/Crime%20in...), violent crime clearance rate was ~50%, murder ~64%. And Missouri overall might be a good proxy for the US in general, we have everything from two old urban centers to the most rural of areas. So, yeah, you could well be right in #0, and you're certainly right with #1.