When I teach my writing classes and students are struggling with finding evidence to support their topic, I normally suggest they start with a broad Google search and begin to narrow the results down from there.
However, one of the better ways of quickly finding relevant information is to look at the bottom sections of a Wikipedia article--References, Further Reading, and External Links. Wiki is a summary, however, the information for the summary is listed at the bottom so you can go directly to the original source for first hand information. This helps too in sorting reliable from unreliable sources as well as giving one a variety of original sources if you're comparing and contrasting opposing sides of an issue.
For your particular topic at hand, do you have time to go beyond internet searches for information? You could visit your local police station to see if an officer or detective would be available to interview regarding this topic as it relates to law enforcement. Additionally, the fraud department of a bank may also be an excellent place to find folks who can give you first hand information or even point you to various websites that would give you reading material for your topic. In regards to answering "what is acceptable and what is not", that might be something to ask a criminal lawyer about or ask a law office what resources online would provide clarity for the subject.
I hope this is helpful in locating relevant and informative articles for your essay!
