While assigned to St. Elisabeth of Hungary Church in Denver, Colorado, Heinrichs was fatally shot while distributing communion.

Under persecution from Otto von Bismarck's Kulturkampf, the Franciscan province of St. Elizabeth of Hungary fled their monastery in Fulda and settled at St. Bonaventure Friary in Paterson, New Jersey.

On December 4, 1886, Heinrichs entered the Franciscan novitiate at St. Bonaventure and received the monastic name Brother Leo.

[5] He had received permission to return to Germany to visit his family after an absence of over twenty-one years; but postponed his journey until after June 7, 1908, when he planned to give First Communion to a class of seventy children.

A week before his death, he preached at the Young Ladies' Sodality meeting, remarking, “How sweet it is to die at the feet of Mary.”[1] Heinrichs normally celebrated the 8 AM Sunday Mass, but on Sunday, February 23, 1908, as he had a meeting scheduled that day, he switched with the priest Wulstan Workman to take the 6 AM "Workingmen's Mass.

Heinrichs first attempted to retrieve the fallen Host and collapsed mortally wounded on the step of the Altar of Our Lady,[4] and died minutes later.

Off-duty Denver police officer Daniel Crefin (or Cronin) arrested Alia after a brief struggle on the church steps.

"[7] In the face of rumored threats of summary justice, Denver law enforcement moved Alia to Colorado Springs for his protection.

However, Denver police officers expressed a belief that local anarchists had smuggled the knives Alia had used into the Colorado State Penitentiary.

"[12] Despite the Franciscan Order's pleas, Giuseppe Alia was hanged on July 15, 1908, at the Colorado State Penitentiary in Cañon City.

The night noises of the penitentiary had died away when Warden Cleghorn summoned the murderer from his cell, and through an interpreter, told him that the hour of his death had arrived.

Then he raised his head, uttered a string of oaths, and offered his best physical resistance to accompanying the guards to the gallows.

[13]After a Solemn High Mass of Requiem in Denver, Heinrichs' body was transported by rail to St. Bonaventure Monastery in Paterson, New Jersey.

Michele Presutto notes that the murder occurred at a time of anti-Marxism, anti-anarchism, and anti-Italian sentiment, but he attributes the roots of Alia's anti-clericalism to the rivalry between the Catholic priesthood and Waldensian Protestant missionaries in Sicily.

Secretary of Commerce and Labor Oscar Straus ordered immigration inspectors to work closely with local police and the United States Secret Service to find, arrest and deport immigrants with Anarchist beliefs under the terms of the Anarchist Exclusion Act.