According to a statement from the Holy See’s press office director, Fr. Fredrico Lombardi, “[a] note found on the scene is currently being studied by Vatican magistrates” while they await the results of an autopsy.
Fr. Lombardi also noted that “[Alessandro’s] behavior had not, until now, given cause for concern” and that he had passed “the usual psychological aptitude selection process,” as well as “[the tests] concerning the handling of weapons” this past April.
While Benedetti's death has aroused memories of the 1998 Swiss Guard tragedy—when a corporal in the Swiss Guard killed the Swiss Guard commander and his wife before turning his gun on himself—it seems that the motivations are quite different.