Whether illegal immigrants bring a significant amount of crime to the United States is one of the most important questions to answer in the debate over immigration policy. President Trump also seems to think so as he launched his campaign in 2015 with the now infamous quote: “[Mexican illegal immigrants] are bringing drugs. They’re bringing crime. They’re rapists. And some, I assume, are good people.” From executive orders to major talking points to the President’s speeches, which Vox reporter Dara Lind has aptly described as “immigrants are coming over the border to kill you,” Trump is interested in this important topic. 

It is difficult to know whether illegal immigrants are more likely to commit crimes than native-born Americans are. All immigrants have a lower criminal incarceration rate and there are lower crime rates in the neighborhoods where they live, according to the near-unanimous findings of the peer-reviewed evidence. Since 1911, large nationwide federal immigration commissions have asked whether immigrants are more crime-prone than native-born Americans and each one of them answered no, even when the rest of their reports unjustifiably blamed immigrants for virtually every problem in the United States. From the 1911 Immigration Commission, also known as the Dillingham Commission, to the 1931 Wickersham Commission, and 1994’s Barbara Jordan Commission, each has reported that immigrants are less likely to commit crimes than native-born Americans. 

That research combines legal and illegal immigrants to calculate a crime rate for all immigrants, but the modern debate is over the crime rates of illegal immigrants. Most people seem to accept that legal immigrants have lower crime rates than natives. Measuring illegal immigrant crime rates is challenging for several reasons. First, the American Community Survey does not ask which inmates in adult correctional facilities are illegal immigrants. Second, federal data on the number of illegal immigrants incarcerated on the state and local level is recorded through the State Criminal Alien Assistance Program (SCAAP), which is a combination of stocks and flows that is incomparable to any other measure of inmates. Third, 49 states do not record the immigration statuses of those in prison or convicted. Until recently, these data limitations allowed pundits to say anything about illegal immigrant crime without fear of being fact-checked. 

Cato scholars have since published numerous Immigration Research and Policy Briefs to shed light on this topic. Michelangelo Landgrave, a doctoral student in political science at the University of California, Riverside, and I released a paper today that estimates that illegal immigrant incarceration rates are about half those of native-born Americans in 2017. In the same year, legal immigrant incarceration rates are then again half those of illegal immigrants. Those results are similar to what Landgrave and I published for the years 2014 and 2016. We estimated illegal immigrant incarceration rates by using the same residual method that demographers use to estimate the number of illegal immigrants in the United States, only we also applied that method to the prison population. We used the same method to also find that the incarceration rate for young illegal immigrants brought here as children and theoretically eligible for deferred action is slightly below those of native-born Americans.

The second strand of research from Cato looks at criminal conviction rates by immigration status in the state of Texas. Unlike every other state, Texas keeps track of the immigration statuses of convicted criminals and the crimes that they committed. Texas is a wonderful state to study because it borders Mexico, has a large illegal immigrant population, is a politically conservative state governed by Republicans, had no jurisdictions that limited its cooperation with federal immigration enforcement in 2015, and it has a law and order reputation for strictly enforcing criminal laws. If anything, Texas is more serious about enforcing laws against illegal immigrant criminals than other states. But even here, illegal immigrant conviction rates are about half those of native-born Americans – without any controls for age, education, ethnicity, or any other characteristic. The illegal immigrant conviction rates for homicide, larceny, and sex crimes are also below those of native-born Americans. The criminal conviction rates for legal immigrants are the lowest of all.

The Texas research is consistent with the finding that crime along the Mexican border is much lower than in the rest of the country, homicide rates in Mexican states bordering the United States are not correlated with homicide rates here, El Paso’s border fence did not lower crime, Texas criminal conviction rates remain low (but not as low) when recidivism is factored in, and that police clearance rates are not lower in states with many illegal immigrants – which means that they don’t escape conviction by leaving the country after committing crimes. 

SCAAP is a flawed source of data for several reasons, but even it shows that illegal immigrants have lower incarceration rates than native-born Americans. Based on estimates of the non-citizen population going back to 1955, they are less likely to be arrested for homicide. Federal incarcerations and convictions reveal little here because they represent less than 8 percent of all incarcerations and, worse still, are not representative of nation-wide crime trends. In 2016, for instance, there were only 85 federal convictions for murder out of a nationwide total of 17,785 murder convictions that year, comprising less than 0.5 percent of all murders. Government immigration enforcement programs like E‑Verify may even raise crime rates.

Cato scholars aren’t the only folks investigating illegal immigration and crime. Sociologists Michael Light and Ty Miller found that a higher illegal immigrant population does not increase violent crime rates. Those two researchers then teamed up with Purdue sociologist Bryan C. Kelly to look at how higher illegal immigrant populations affected drug arrests, drug overdose deaths, and DUI arrests. They found large and significantly associated reductions in drug arrests, drug overdose deaths, and DUI arrests with no significant relationship between increased illegal immigration and DUI deaths. 

None of what I wrote above will console a victim of illegal immigrant crime – and it shouldn’t. To those victims and their loved ones, their pain is not diminished by knowing how unlikely it was to happen to them. There will be criminals in any large group of people and there are some infuriating and shocking anecdotes. The public seems to understand that the actions of a comparatively small number of illegal immigrants do not mean that they are more crime-prone than native-born Americans – which is what matters the most when debating public policy. A 2016 Pew poll found that only 27 percent of Americans thought that illegal immigrants were more likely to commit serious crimes than native-born Americans, while 67 percent said less likely. Among Republicans, 42 percent said that illegal immigrants are more likely to commit serious crimes and 52 percent said less likely. A Quinnipiac poll in 2018 revealed that only 17 percent of voters thought that illegal immigrants committed more crimes than native-born Americans and 72 percent of voters thought that illegal immigrants committed less crime. 

Part of the reason why native-born Americans might not be concerned as much with illegal immigrant crime overall, but very concerned in some specific cases, is that most illegal immigrant criminals probably victimize other illegal immigrants. Of the homicides in 2015 where the relationship between the murderer and the victim is known, about 80 percent of murderers knew their victims. The relationship between victim and murderer could be even higher for illegal immigrants. Americans tend to care more when native-born Americans are murdered by illegal immigrants than when an illegal immigrant murders another illegal immigrant.

The debate over illegal immigration and criminality will likely continue until much better data are available across the United States. Based on the research above, I’m fairly confident that illegal immigrants are less likely to be criminals than native-born Americans. On the overall issue of immigration and crime, the evidence is so one-sided that even Mark Krikorian, executive director of the Center for Immigration Studies, has said that, “A lot of data does suggest immigrants are less likely to be involved in crime.” This issue will be resolved when states and localities keep better records of the immigration statuses of people convicted in their states – just like Texas does. The crime data are so complicated and inconsistently kept that even the government misinterprets its own data. The government should resolve these data issues.