He may have sought to open the coffin to see if there was even a body in it. Considering the history of the unroyal Mrs. Elizabeth Alexandra Mary Battenberg/Mountbatten it is anyone's guess what is in that coffin.
Chaos Erupts as Man Charges Queen’s Casket – Dragged Out of Room by Police
The somber ceremony of Queen Elizabeth’s lying in state was shattered Friday night when a man left the long line of mourners filing through Westminster Hall and rushed the casket.