- how accurate that "piece of paper" probably is
- the likely informant of that "piece of paper"
- what other "pieces of paper" have to say
- how reasonable the information on that "piece of paper" is
There's more to making a case than this, but these are elements of analysis that should be considered on a regular basis. And if at all possible, try and find other "pieces of paper" that mention the same date, location, or relationship. Ideally those pieces of paper will have different informants-preferably ones who had first hand knowledge of the information.