Unfortunately, the comments of Donald Trump have sucked the oxygen out of the public debate on the significance of such crime trends. According to new data from the United States Sentencing Commission. While crimes by illegal immigrants are slightly down (38.6 percent of all federal sentencings in 2013 but 36.7 percent in 2014), they still represent a huge percentage of such offenses in the federal system given that they represent an estimated 3.5 percent of the U.S population. There is available data from the states, though individual states likely have figures.
This includes 20 percent of the kidnapping/hostage taking sentences in 2014 and 12 percent of the murder sentences. Another 19.4 percent of national-defense related sentences are attributed to illegal immigrants.
If you combine both illegal and legal aliens, the population represents almost half of all sentences — 42 percent of all federal sentencing in 2014.
These figures are according to the Washington Examiner and have been reported on other sites. I went and looked at the Sentencing Commission report and confirmed the figure on non-citizens but I could not locate the specific numbers on illegal immigrants. If anyone has a link, it would be great to add it. Here are the general sourcebook tables from the United States Sentencing Commission.