On February 20, 1915, Henry and Mary Ellen Webb, who had married the previous June, began quarreling at their home at 628 Paulson Avenue in Larimer. The quarrel reportedly centered on money. Mary is said to have threatened to leave her husband, who worked at a hotel, for another man due to his inability to support her.

When the quarrel escalated the next day, Mary Webb struck her husband with a poker and he responded by slashing her, fatally, with a razor. He then fled the scene. Webb was arrested hours later. He confessed to police and led them to the murder weapon.
Newspaper accounts report that Mary Webb was the daughter of a prominent family and was so well liked that threats of lynching were directed toward Webb when he was arrested.

At trial, Webb’s attorney argued that Webb had acted in self-defense and that the evidence justified a manslaughter verdict. He was convicted of first degree murder on June 18, 1915, and sentenced to death on September 2.
Webb appealed his conviction; in a lengthy appellate opinion (Commonwealth v. Webb, 252 Pa. 187, 1916), his self-defense claim was rejected on the grounds there was no evidence he was injured during the quarrel and no evidence her provocation was sufficient to justify lethal self-defense.

His pardon request also rejected, Henry Webb was executed on May 2, 1916, the first African American in Pennsylvania to die in the electric chair.