The Amistad Committee was painfully aware that the President's policy aimed at condemning the African captives to permanent slavery, or possibly death, and the abolitionists worked out a defense strategy to ensure that the verdict did not go against them. They built up a case around the argument that the Africans were not legally slaves, as they had been brought to Havana and sold there contrary to the Anglo-Spanish Treaty of 1820, which prohibited the transatlantic slave trade. This treaty had been re-affirmed in 1835 and followed by a Royal Order from the Queen of Spain in 1838 directing the Captain-General of Cuba to enforce the law with "the strongest zeal."

This line of defense was strengthened by a deposition made by Dr. R.R. Madden, a native of Ireland, who had served the British government in the Gold Coast (Ghana) and in Havana, Cuba, as a Commissioner on the Court of Mixed Commission for suppressing the slave trade. Dr. Madden revealed that flagrant violations of treaty stipulations regarding the slave trade were openly sanctioned by the Spanish Captain-General and other government officials in Cuba, and that the American Consul there, Nicholas Trist, was a collaborator who reaped huge financial benefits from the slave trade. Dr. Madden came to New York in November and met with Lewis Tappan. He went to see the captives at New Haven and proceeded to Hartford to give evidence at the trial. Since the trial had been deferred, he had to give testimony to Judge Judson in chambers.

Dr. Madden argued that the Amistad captives were recent importees. On the licenses for transporting them from Havana to Puerto Principe, they had been entered as Ladinos, i.e., slaves brought to Cuba before 1820. But Madden pointed out that this type of forgery was common practice in Cuba and that Ruiz' and Montez' papers of ownership were not legally valid.

About this time, Ruiz and Montez were arrested in New York on charges of assault, kidnapping, and false imprisonment, brought against them on behalf of two of the Africans. Lewis Tappan, the real leader of the Amistad Committee, was blamed for this action, which horrified political conservatives. Bail was fixed at $1,000 each. Montez paid immediately and departed for Cuba. Ruiz chose to enlist sympathy by staying in jail. The Spanish Minister immediately protested to the State Department that for alleged offenses committed in Cuba, the U.S. Courts had no jurisdiction. The Secretary of State, Forsyth, instructed the District Attorney to render every possible assistance to the Spaniards. The abolitionists were accused of "making sport of the law...." It was a tactical error on the part of the abolitionists, and it cost them some support from moderates. But Ruiz finally got tired of confinement, paid the bail, and returned to Cuba. Ruiz and Montez were both absent at the final hearing.