IT HR:One other thing to remember is that courts will look more favorably in your direction if you start the investigation within a timely manner. A couple of recent court cases I have seen talked about this being with in 24 hours of you learning about an alleged incident. The courts say you have a duty to investigate and that duty means investigate it now and not when you feel like it or when you get time. Starting the investigation right away shows that you are taking the allegations seriously and want to get to the bottom of the issue.
Essentially, when you permit a delay, you are communicating that it is acceptable to you that (alleged) harassment continue until you have time to deal with it. Put another way, saying that you'd rather wait until tomorrow is like saying you'd rather allow sexual harassment (potentially) to continue until tomorrow.
One of the big things in investigations, since we're getting into specifics about investigations rather than resources, is to understand what, exactly, it is that you are investigating. In a harassment case, the questions to investigate are things like, "What was the behavior that was alleged to have been harassment (or a violation of the company's anti-harassment policy, which is usually more strict than the legal standard of sexual harassment)", "Who witnessed the alleged harassing behavior", "When did the reported behaviors occur," and "Where did the reportedly harassing behaviors occur"? I've seen investigatory notes that were merely stream of consciousness typing that didn't necessarily help. When you have a complaint, understanding what the questions are that you are trying to answer by investigating will help keep your investigation on track. A lot of times, it's important to see how the answers to these questions mesh. You can end up with strange situations like a bus boy reportedly harassing a waitress, reportedly in full view of the waitresses' best friend....on the roof of the building next door during working hours. That should lead you to question things like, why were they on the roof? Why were they on the building next door?
More than once in your career you will find in the course of your investigation that the complainant has violated policies and you should enforce company policy evenly, without regard for whether or not the harassment complaint was substantiated, unless the policy violations are related to, for example, steps the employee took to avoid harassment, such as hiding in the bathroom, possibly constituting unapproved absence from his or her work station.