The Fritz Contzen v. United States case in 1900 revolved around a dispute over land ownership. Fritz Contzen claimed that he had purchased the land from Mexican citizens who were granted the property by Spain before it ceded Florida to the U.S. However, his claim was challenged by the U.S., which argued that there was no valid grant of this land from Spain to any private individual or entity prior to its transfer of Florida's sovereignty. Contzen presented several documents as evidence, including an alleged Spanish grant and various affidavits attesting to its authenticity and validity. Despite these efforts, both lower courts ruled against him on grounds of insufficient proof regarding the original Spanish grant's existence and legitimacy. Upon reaching Supreme Court, it upheld these rulings stating that not only did Contzen fail to provide conclusive evidence for his claims but also noted significant inconsistencies within his submitted documents themselves - such as discrepancies in dates which cast further doubts on their credibility. Therefore, due lack of convincing proof supporting Contzen’s assertions about rightful ownership through a legitimate Spanish Land Grant predating American control over Florida; The Supreme Court affirmed previous decisions favoring United States’ stance.

The dissenting opinion in the case of Fritz Contzen v. United States argued that the defendant, a German citizen residing in Mexico, should not have been extradited to face trial for forgery charges in Texas. The dissenting justices believed that there was no valid extradition treaty between the U.S and Mexico at the time of Contzen's arrest and thus his detention violated international law. They also disagreed with majority’s interpretation of an 1861 treaty between Prussia (of which Germany was part) and U.S., arguing it did not cover offenses committed outside either country by non-residents or citizens living abroad. Furthermore, they contended that even if such a treaty existed, it would be irrelevant as Mr.Contzen was arrested before its ratification by both countries' governments. Therefore, they concluded that Mr.Contzen's extradition from Mexico to Texas had no legal basis under existing treaties or international law.