The letter President Trump drafted in May to explain his reasoning to terminate James Comey as FBI Director was never sent to Comey, but was instead given to deputy attorney general, Rod Rosenstein, who then wrote the final memo explaining to the public why Comey was fired.
Currently, Rosenstein is overseeing special counsel Robert Mueller's investigation regarding Russia's influence in the 2016 election, in addition to whether Trump obstructed justice. Mueller's team has obtained the original letter drafted by Trump, which is believed to have candid insight into why Comey was actually fired.
Trump met with Rosenstein on May 8 at an Oval Office meeting and Trump gave a copy of the original letter to Rosenstein. Rosenstein in turn then agreed to write the memo that was used to explain Comey's firing.
Rosenstein's memo arrived at the White House on May 9 and an aide attempted to deliver the memo to FBI Headquarters in Washington, D.C., according to the New York Times. Comey was unable to accept the letter because he was in California and eventually learned he had been fired from a breaking news report on TV and was later officially informed in a phone call.
The Trump administration has provided numerous explanations for firing Comey since May, including that the president had lost confidence in Comey's ability to lead the FBI and that Comey had not handled the Clinton email case properly, which was the reason outlined in the Rosenstein memo.