Immigrant criminality and its impact on the United States is one of the most important issues in the public debate over immigration. In order to provide new insight into this topic, my coauthor Michelangelo Landgrave and I have attempted to estimate the illegal immigrant incarceration rate. I have also written a short paper on Texas criminal conviction rates by immigration status and crime based on data provided by the state of Texas. All three papers found that illegal immigrants were less likely to be convicted or incarcerated for crimes than native-born Americans.

My paper on illegal immigrant crime rates in Texas is based on data from the Texas Department of Public Safety (DPS) that I obtained through a Public Information Act request. The Texas DPS data separately show the number of convictions and arrests of illegal immigrants, legal immigrants, and native-born Americans for 44 and 46 different crimes, respectively, in the state of Texas by year from January 1, 2011, to November 15, 2017.

One of the persistent criticisms of my paper on Texas criminal conviction rates is that the DPS data do not record the number of illegal immigrants who commit crimes but are not convicted. Given data limitations, that is probably an impossible question to answer in a satisfactory way for immigrants and for natives. However, I try to address this criticism in my Texas paper by showing that the gap between the arrest rates and conviction rates for illegal immigrants and the gap between the arrest rates and conviction rates for native-born Americans are similar, indicating that there are few illegal immigrants who are arrested for offenses who then disappear or are deported before their convictions relative to natives who are arrested and then not convicted.

A related criticism is that illegal immigrants flee Texas and then go back to their home countries after they commit crimes, which means that the Texas state conviction data would not count them. Thus, the criminal conviction rate for illegal immigrants is so low because they commit their crimes and flee – an option that few native-born American criminals possess. This argument makes a certain amount of sense in Texas as it shares a long border with Mexico, the source of a majority of illegal immigrants in Texas.

To answer that second criticism, we decided to investigate whether police clearance rates are correlated with the number of illegal immigrants on the state level. According to the FBI’s Uniform Crime Reporting (UCR) Program, law enforcement agencies can clear offenses by one of two means. The first is called “cleared by arrest” whereby a person must be arrested, charged with an offense, and turned over to a court for prosecution. The second is called “cleared by exceptional means,” whereby the police must identify the offender, gather enough evidence for an arrest and to charge them with a crime, identify the offender’s exact location, and have encountered a circumstance out of law enforcement’s control that prevents an arrest. The death of the offender or the lack of an extradition treaty with the country harboring a suspected criminal are common causes of clearances by “exceptional means.” Mexico and the United States have an extradition treaty. An offense is cleared when the police have taken certain actions to solve the underlying crime short of a criminal conviction.

Landgrave ran many regressions between clearance rates (logged) and the proportion of the population of each state who were illegal immigrants (logged) with state-year and region-year fixed effects. The regressions control for demographic characteristics, the number of police officers for every 100,000 residents, education, and population density. He ran regressions for clearance rates by major crime and the entire crime index. All he found is that motor vehicle theft and burglary clearance rates are positively correlated with the proportion of the population who are illegal immigrants, but only at the 10 percent level for the state-year fixed effects (Table 1, click for larger version). There were no other statistically significant results.

Table 1: Correlation between State Police Clearance Rates and Illegal Immigrant Population

As a quick exercise to test this persistent criticism, these results reveal that there is no nationwide link between clearance rates and the proportion of the population who are illegal immigrants. The only exception is that police clear more motor vehicle and burglary offenses in states with more illegal immigrants as a proportion of their population, but only in one permutation and only at the 10 percent level. Although the theory that illegal immigrants commit crimes and then flee states seems plausible, we see no evidence of that in the aggregate clearance rates.