The answer to this depends to a large degree on the audience for your investigative report. However, it is generally best to avoid jargon when at all possible.
If your audience is made up of specialists in the field that you are investigating, it can be perfectly appropriate to use jargon. All of the members of your audience will understand what you are saying. In fact, it may even help you to communicate with them because they may have come to think in terms of jargon.
However, unless you are writing for such an audience, it is better to avoid jargon. For one thing, using jargon can allow you to not think as clearly as you should. You might just be using “typical” terms without really thinking about how you are using them. It is better to use plain English so that you have to think clearly and make sure that what you are saying is accurate. More importantly, using jargon can make your report inaccessible to most people. If anyone in your audience or your potential audience is not a specialist, you must not use jargon so as to avoid making your report unintelligible to them.