In a situation like this (where you aren't looking for a particular case, just a type of case), it may be best to use open web resources or the search box on the library home page to start your search. This will help you find articles or web sites that mention cases of interest that you could then find out more about in our legal databases. For instance, check out the news feed on criminal justice headlines from the American Bar Association.
Another idea is to examine local news. Try visiting your local newspaper's website and searching using its search feature with terms like "criminal case" or "not guilty plea," or try searching for particular criminal terms such as "aggravated assault" or "involuntary manslaughter." Make sure these phrases are in quotes to properly narrow your search.
After you've found a case that interests you, you can then use a legal database such as Nexis Unito search for the actual case by party (see directions here).