NPR didn't do the research, they simply reported on it. Research was done at Stanford Univ. and by CATO institute (libertarian and right leaning).
Some quotes, because you didn't bother to read the article.
"Some of the most
extensive research comes from Stanford University. Economist Ran Abramitzky found that since the 1960s, immigrants are 60% less likely to be incarcerated than U.S.-born people."
"There is also state level research, that shows similar results: researchers at the CATO Institute, a libertarian think tank,
looked into Texas in 2019. They found that undocumented immigrants were 37.1% less likely to be convicted of a crime."
Also, might add that I'm not ignoring the crime, but crimes by illegal immigrants are not an existential crisis for our country; you're far more likely to be a victim of crime perpetrated by a US citizen than by an illegal immigrant.