The reporters had to check police reports and documents about the number of violent crimes reported by Memphis City Schools. I find this article very interesting because it brings to light a good story, but doesn't say how they determined the number of crimes that went unreported. If the crimes are unreported, then there are no police records of them. Perhaps the school keeps records of conflicts brought to their attention by students, teachers and parents. I don't know if these kinds of records are public, because they concern individuals and probably information that would be considered private.
This paragraph is essential in expressing the story:
"This year, the schoold district told the state about 12 violent crimes against students. They should have reported at least 38. Last school year, the district also reported 12 violent crimes, though the real total is at least 84. In the 2006-2007 school year, the state learned about 2 crimes against students, though we found at least 96 cases should have been reported."
However, it does not say where they got the unreported numbers from.
The reporter would have to know how to access and use public documents. Some police reports can be found on the web, so they would need the skills to locate those. Otherwise, they would have to know where and how to get the police records. The reporter also probably found a lot of their contacts via the internet through school websites and the police website. The reporter would have to locate the possible contacts and obtain their contact information.