Secondary and even primary sources can be fraudulent, inaccurate, or biased. Eyewitness accounts may be purposely distorted in order to avert blame or to bestow praise on a particular individual or group. Sometimes, the closer you are to an event, the more emotionally involved you are, and this distorts your understanding of it. We can all recall events in which we completely misunderstood the feelings, actions, and even words of another person. Historians have to weigh evidence carefully to see if those who have participated in an event understood it well enough to accurately describe it, and whether later authors understood the meaning of the primary sources they used.
Official statements present another problem that of propaganda or concealment.
A government, group, or institution may make statements that it wishes others to believe but that are not true. What a group says may not be what it does. This is especially true in politics. Historical research always involves checking one source against another. It might turn out, for example, that parts of each account are correct and other parts are distorted in some way.