The unexpected firing of FBI Director James Comey was accompanied with an explanation that troubled many due to it's contradiction of prior statements made by President Trump and Attorney General Jeff Sessions. 

In May, Sessions sent Trump a memorandum which cited previous incidents involving Comey the department found concerning. 

"The Director was wrong to usurp the Attorney General's authority on July 5, 2016, and announce his conclusion that the case should be closed without prosecution," the memo said regarding a press conference given by Comey wherein he stated Hillary Clinton should not be subjected to a criminal prosecution.

However, in October — just days before the election — Comey delivered a statement where he said the case into Hillary Clinton's emails should be re-opened due to new evidence. This statement was also included in the memo. According to Deputy Attorney General Rod Rosenstein, Comey's actions as director were inappropriate. 

Based on the memos sent by the Department of Justice, Trump decided firing Comey was the best decision.