Ordinarily, a person who starts into motion the events with a suicide intent ultimately commits suicide even though the mechanism might be not what he intended. That he was shot on the way to certain death nine stories below probably would not change his mode of death from suicide to homicide, but the fact that his suicide intent would not have been achieved under any circumstance caused the medical examiner to feel that he had homicide on his hands. . .
Note that regardless of whether it's true or false, the narrative is lent credibility by the fact that it's told from the point of view of a medical examiner trying to determine whether or not a crime was committed.
From this point on, it reads much like a detective story:
Further investigation led to the discovery that the room on the 9th floor from whence the shotgun blast emanated was occupied by an elderly man and his wife. He was threatening her with the shotgun because of an interspousal spat and became so upset that he could not hold the shotgun straight. Therefore, when he pulled the trigger, he completely missed his wife, and the pellets went through the window, striking the decedent.
When one intends to kill subject A, but kills subject B in the attempt, one is guilty of the murder of subject B. The old man was confronted with this conclusion, but both he and his wife were adamant in stating that neither knew that the shotgun was loaded. It was the longtime habit of the old man to threaten his wife with an unloaded shotgun. He had no intent to murder her; therefore, the killing of the decedent appeared then to be accident. That is, the gun had been accidentally loaded. . .
Accidentally loaded? By whom? The plot thickens (i.e., gets murkier).