Early on the morning of February 2nd, 1915 Werner Vanhorn crept towards the Canadian Pacific Railway Bridge which spanned the St. Croix River, the international boundary between Canada and the United States, from St. Croix on the New Brunswick side of the bridge to Vanceboro, Maine on the American side. Carrying two suitcases full of dynamite he waited until after a passenger train crossed the bridge before sneaking onto the bridge. The bridge itself was a modest 150ft long truss span bridge made of steel. Setting about his work he quickly placed the dynamite on the end post of the north truss on the New Brunswick side of the bridge. He then quickly detonated the dynamite before fleeing to the American side of the border. However, Vanhorn was not much of a saboteur and his bomb caused little damage. In fact, trains ran across that same bridge later that day.

He was quickly arrested at his hotel in Vanceboro and charged with damaging the American side of the bridge from the shock of the explosive. Vanhorn claimed to be a German agent who had escaped from a military prison in Halifax and that his actions were legal since Canada and Germany were at war. Canada immediately petitioned for Vanhorns return but Canadian officials feared that American neutralist policies would prevent his extradition. Ironically those same policies meant that the bridge that Vanhorn tried to blow up could not be used for transporting military personnel or military equipment. All military personnel and equipment instead had to be hauled along the Intercolonial Railway line which was hundreds of miles away.

Vanhorn had hoped that by attacking the Canadian side of the bridge and then fleeing to the American side that he could then seek sanctuary in the United States. However, after spending 30 days in jail for damaging the American side of the bridge and while facing more charges of transporting dynamite illegally through the United States he lost his long extradition battle and was extradited to Canada in 1919. He was eventually found guilty of attempting to blow up the St. Croix Bridge and was sentenced to 10 years in Dorchester Penitentiary. Vanhorn could not prove that he was a member of the German army and therefore could not qualify for protection from prosecution under provisions of the Hague Tribunal.