Contacts = Necessity
Good investigative reporters have contacts in the places most likely to provide stories. Your contacts do not have to be people at the top of departments or companies. In fact, people down the ladder are often more practical use. Identify people in key positions within organisations. Good contacts are people like court clerks, council clerks, company clerks--in fact, clerks almost anywhere. There are the people who see all sorts of information you might find useful.
I found this reading really useful for my preparation of investigative report on the retail season. Initially, I was planning to interview a few managers at local businesses, but now I feel like I can have a little more breathing room, because it might be useful to interview regular employees too.
However, it seems like our investigative reports are going to be a little different, because a lot of us (including me) will need to actually research our topic. We really can't rely solely on interviewing people in this case, because we need to include more than simply a poll on a subject to uncover people's opinions. Facts are more important, because our investigative report could easily sway into a feature article if the right amount of facts are not included in the piece. Regardless, like this website says, contacts are of the essence. The more contacts we have, the easier it will be to write a story, because quotes really do write the stories for us.