[5][6] At the time of the 1940 United States Census, he was living in East Chicago with his mother Antonia and his stepfather Martin Gzik.

[7] While in college, he played at the end position for the 1943 Michigan Wolverines football team that compiled an 8–1 record and was ranked No.

[8] While still serving in the military as a lieutenant in the Marine Corps, Mroz married in October 1945 to Shirley Gamm at the Mt.

On November 1, 1950, Mroz engaged in a gunfight with two Puerto Rican nationalists who were storming Blair House in an assassination attempt on President Truman, upstairs in his quarters.

After hearing the gunshots, Mroz ran through a basement corridor and stepped out of a street-level door on the east side of the House, where he opened fire on Collazo, shooting him in the chest and dropping him.

[14] After the shooting ceased, Mroz discovered the body of the second attacker, Griselio Torresola, in the hedges adjacent to Blair House.

[2] In December 1951, President Truman, described as being "deeply moved," decorated Mroz and Floyd Boring with silver lapel buttons for their roles in saving him.

He said they were "two straight-shooting secret service agents" and gave them [17] Collazo survived and was put on trial in February 1951.

[2][19] From 1960 to 1962, Mroz was the chief of the Charleston, West Virginia office of the Secret Service, where he gained note for his investigation of a counterfeiting ring.