A 2018 U.S. Government Accountability Office study of non-citizens in U.S. prisons and jails during 2010 to 2016 found that they had been arrested or transferred for 33,300 homicides committed within the U.S. during 1964-2017. This study double-counts some homicides because the "data did not allow" the study to "distinguish between a new arrest and a transfer from one agency to another." However, it fails to count many other murders because (1) it only covers "a portion of the total population of criminal aliens incarcerated at the state and local level" since there "are no reliable population data on all criminal aliens in every U.S. state prison and local jail," and (2) it cannot identify murders that don't result in arrests, and 38% of all murders in the U.S. go unsolved. This rate is higher for minorities, and in the sanctuary city of Chicago, it was 83% in 2017.