Henry Rathbone and his wife Clara joined Abe and Mary Lincoln on April 14th, 1865 at Ford Theatre. Little did they know that John Wilkes Booth had other plans for them. Henry lived with survivor's guilt his entire life after the assassination, and let this guilt drive him to madness.

Sources:

https://www.nyhistory.org/blogs/attending-fords-theater-with-the-lincolns-the-tragic-lives-of-clara-harris-and-henry-rathbone

https://allthatsinteresting.com/henry-rathbone

https://www.thegettysburgexperience.com/a-christmas-murder