Trump is exaggerating how many people illegally cross the border. Moreover, most independent research contradicts the idea that illegal immigrants bring more crime. A 2018 study published in the peer-reviewed journal Criminology, led by Michael Light, a criminologist at the University of Wisconsin at Madison, examined whether places with higher percentages of undocumented immigrants have higher rates of violent crime such as murder or rape. The answer: States with larger shares of undocumented immigrants tended to have lower crime rates than states with smaller shares in the years 1990 through 2014.