[2] At the outbreak of World War I, Werner Horn was a German reserve army lieutenant who had been in Moka, Guatemala, as the manager of a coffee plantation.

He found work at another plantation in Salto de Agua, Chiapas, but before he could leave, he received a card telling him to return to Germany.

Von Papen was seeking saboteurs to disrupt Canadian railways and thought that Horn, who was eager to serve the fatherland, was an ideal candidate.

[1] Horn left New York from Grand Central Terminal on a New Haven Railroad passenger train to Boston on January 29, 1915, carrying a suitcase of dynamite.

Horn spent the next two days maintaining a low profile and watching the extremely-busy Canadian Pacific Railway main line to determine the schedule of trains.

He apparently changed into a German army uniform to avoid being convicted of being a spy (and potentially executed) before proceeding to the railway bridge over the St. Croix River sometime after midnight.

[7] Horn proceeded to position a suitcase filled with explosives on the Canadian side of the bridge but was interrupted by an oncoming train and was forced to move out of its path.

The sheriff of Washington County (for Vanceboro), along with two Canadian police officers from McAdam, New Brunswick, who crossed the border to provide assistance, detained Horn at the hotel.

Horn reportedly changed into his German army uniform (to avoid being arrested as a spy, which was an executable offence) and surrendered to American authorities.

[7] Horn was moved soon thereafter to a jail in Machias, Maine for his safety (Vanceboro residents were upset with him over the damage that he had caused them) while Canadian authorities began the process of seeking his extradition.

Horn was interrogated by the Bureau of Investigation for several days and signed a confession with an agreed-upon statement of facts in which he revealed the details of his crime.