Was King David assassinated? A credible scenario from 1-Kings-I-II regarding the accession of Solomon

The anti-Solomonian pamphlet which is underlining 1 Kings 1-2 shows that th e accession of Solomon to the throne arises from a coup. The designation of Solomon by David could have been extorted by Nathan, then the aging king c ould have died the very same day. Later, Adonias and Joab could have been p ut to death. How does the ancient author know what happened behind the wall s of the palace? He can only have imagined some of the scenes. For other sc enes, he is probably bound by official information from the new power, whic h is looking towards having Solomon being seen as the true heir of David. B y the way, we are not sure that Solomon is his son, and the scenario of the tale is not credible. Therefore, one can ask if the conspirators have not killed the king, then disguised their crime and proclaimed the last suppose d will of the deceased.