During his post-war trials, Monti claimed he had stolen the plane to fight the Germans, was shot down, and joined with partisans, who gave him the SS uniform. His claims were largely believed, resulting in him being court-martialed solely for theft of the aircraft and desertion. On August, 6, 1945, he was sentenced to 15 years in prison. However, on February 11, 1946, Monti's sentence was suspended by
Harry S. Truman, after
Walter C. Ploeser pleaded for leniency on behalf of Monti's parents. As a condition of his commutation, Monti was required to reenlist in the Army Air Forces (later that year, the independent
United States Air Force) as a private, which he did on February 11, 1947. During an interview prior to his arrest, he told the
St. Louis Post-Dispatch that he pretended to be a Nazi "to gain their confidence. I don't like communism and I don't like Russia, but I couldn't be a Nazi. I couldn't have become a Nazi in a year." Meanwhile, Sittler was interrogated by American investigator Anthony Cuomo, and asked Cuomo whether he knew a P-38 pilot named Martin Weithaupt. Cuomo had in fact interrogated Monti. On May 22, 1946, Special Attorney Clyde E. Gooch in Frankfurt, Germany, wrote to
Assistant Attorney General Theron L. Caudle in Washington DC calling for Monti's prosecution. Sittler was brought to the United States in 1946 by the Department of Justice as a witness in the 1947 trial of
Douglas Chandler and the 1948 trial of
Robert Henry Best. Monti, who also knew Chandler and Best, refused to testify against them. He had been summoned on November 18 to the Department of Justice where he was identified as Martin Weithaupt by Sittler, Sittler's wife, and former Nazi propagandist colleagues Margaret Eggers, Loretta Grunau Kapke, and seven others brought to the United States as witnesses against Chandler and Best. Monti had reached the rank of
sergeant by the time he was
honorably discharged on January 26, 1948. Only minutes later, the
Federal Bureau of Investigation arrested him at
Mitchel Field, New York, and charged him with
treason for the propaganda activities performed as "Martin Wiethaupt". On October 14, 1948, a federal grand jury in Brooklyn indicted him for 21 acts of treason committed between October 13, 1944, and May 8, 1945, the
day hostilities in Europe ended. On January 17, 1949, Monti pleaded guilty, surprising the prosecutors and the court, which had prepared for a lengthy trial. Monti's lawyers had advised him to plead guilty, saying there was no hope of an acquittal and that his status as a military officer would constitute a major aggravating factor. They warned him that if he went to trial, he could face life in prison or even execution. Because of the seriousness of the charges, and in light of
Article III, Section 3 of the United States Constitution, the court required testimony despite his guilty plea, and, according to
The New York Times, "Without hesitation, Monti took the witness chair" where he admitted to all the charges. Asked by the judge if he had acted "voluntarily", Monti answered "Yes". His attorney then asked for leniency, citing his upbringing in an extremist and
isolationist environment that "fanatically imbued" him to identify
Soviet Russia and
Communism as the nation's principal enemy. Despite his attorney's appeal for leniency, Monti was sentenced to 25 years in prison and ordered by the judge to pay a fine of $10,000. == Prison sentence ==