If you want to know the truth, you will have to find out. Finding things out is called research. Crudely speaking there are two types of it:
Records research: Records research involves reading written documents, listening to sound recordings (e.g. interviews), and viewing still photography or film footage. The communication in records research is one-way only, from the source to the sink.
Original/live research: Finding out for yourself (i.e. conducting original research), or talking to somebody who found out herself (e.g. a witness to the shooting of U.S. President Kennedy), or talking to somebody who talked to somebody who found out herself (e.g. the grandson of the last survivor of the sinking of the Titanic), and so on. Live research is interactive.
Rigorous research follows a systematic process, the scientific process. It requires a critical mind and doubt, and it produces scientific knowledge. Sloppy research is based on personal observations, personal experience, perceived wisdoms, and anecdotes. It produces traditional knowledge.