Key's son, Philip Barton Key II, followed in his father's footsteps and also became a lawyer, becoming the District Attorney for Washington D.C. In 1858, Key began an affair with Teresa Sickles, the wife of NY Congressman Daniel Sickles. In 1859, Daniel Sickles discovered the affair and after seeing Key outside his home, chased him down and shot him adjacent to the fence at Lafayette Park in D.C.
Sickles became the first person in US to be acquitted of murder due to temporary insanity, and went on to serve as a major general during the civil war where he lost his leg at Gettysburg. Following the war, Sickles took an active interest in preserving the battlefields of the war including Gettysburg. As the National Military Cemetery at Gettysburg abutted the local cemetery, Sickles thought it appropriate to separate the two, and to do so, he procured the old fence from Lafayette Park in DC, where he had shot Key's son.
That is a new story for me. Such nefarious goings on.