Who sent the letter to Imran Khan?

What happened: In a live show by senior journalist Nadeem Malik, he highlighted that the whole letter conspiracy that has been in the political headlines for the past few days is  “Imran Khan is trying to copy Bhutto by waving the letter in the audience. The letter was most likely sent by Ambassador Asad Majeed, about Khan’s visit to Russia, and how it affects the relationship with the US.”  Adding to his statement, Nadeem Malik said,  “Yay sirf Ahtajaji note tha, nothing else! and it was a cipher.”  Details: Subsequently, Nadeem Malik said that the way Imran Khan handled the letter raised a few eyebrows, and it could have been handled in a much more diplomatic manner. Nadeem Malik further talked about,  “Imran Khan used the words that Bhutto previously used, and the letetr could have been handled in a much more diplomatic manner.”  It was noted by Nadeem Malik the statements made by Khan during his speech were controversial and only a political move.