Why did the crime rate go down after immigrants were forced out of Hazelton, PA?

Darcy Lear continues her series on the teaching of "cultures" with this post:

This semester I am teaching the "Spanish & Entrepreneurship" First Year Seminar again and the theme is "Latino Youth." 

To get the semester started, I had students research three towns in the U.S. that had large Spanish-speaking immigrant populations. They were asked to do two things: research the reaction to immigrants and the results of those reactions. 

When one group reported that there had been a drastic drop in violent crime after many Spanish-speaking immigrants had been driven out of Hazelton, PA we had to stop the class to do a meta-analysis of our reactions to that. The first reaction: immigrants were committing violent crimes. 

When I asked what other reasons could be, the first suggestion was that with any drastic decrease in population, crime is bound to decrease proportionately. Nobody's first reaction was that the immigrants were victims of crime. The way information is presented invites us to process it in a certain way. Reporting that after immigrants left a town, violent crime rates dropped suggests a causal relationship--one that most are willing to accept at face value. 

It finally clicked for my students when another group reported that lack of access to financial institutions meant that many immigrants kept most of their money in cash, making them targets of...(wait for it) violent crime!