A Haitian-born doctor based in Florida has been arrested as a “central” suspect in the assassination of President Jovenel Moïse, and the national police chief suggested at a Sunday news conference that he believes the suspect was plotting to become president.

The doctor, Christian Emmanuel Sanon, 63, is now the third Haitian-born suspect with U.S. ties to be arrested.

The Haitian national police chief, Léon Charles, painted Mr. Sanon as a key figure behind the president’s assassination.

“He arrived by private plane in June with political objectives and contacted a private security firm to recruit the people who committed this act,” the police chief said. The firm, he said, was a Venezuelan security company based in the United States called CTU.

“The initial mission that was given to these assailants was to protect the individual named Emmanuel Sanon, but afterwards the mission changed,” Mr. Charles said, implying that Mr. Sanon had meant to install himself as president.

As evidence, Mr. Charles said that Mr. Sanon was the person one of the Colombians contacted after being arrested. During a raid of his home, the authorities said, the police found a U.S. Drug Enforcement Agency cap, a box of cartridges, two vehicles, six pistol holsters, about 20 boxes of bullets, 24 unused shooting targets and four license plates from the Dominican Republic.

A YouTube video recorded in 2011 titled “Dr. Christian Sanon — Leadership for Haiti” appears to present Mr. Sanon as a potential leader of the country. In it, the speaker denounces the leaders of Haiti as corrupt plunderers of its resources.

“With me in power, you are going to have to tell me: ‘What are you doing with my uranium?’” the speaker says. “‘What are you going to do with the oil that we have in the country? What are you going to do with the gold?’”

The night of Mr. Moïse’s death, people who appeared to be arriving to assassinate him shouted that they were part of a D.E.A. operation, according to videos filmed from nearby buildings and synchronized by The New York Times.

Two Americans arrested last week have said that they were not in the room when the president was killed and that they had worked only as translators for the hit squad, according to a Haitian judge who interviewed them. They met with other participants at an upscale hotel in the Pétionville suburb of Port-au-Prince, the Haitian capital, to plan the attack.

The goal was not to kill the president, the two Americans told the judge, but to bring him to the national palace. On Sunday, Mr. Charles said one of the assailants had been given a warrant to arrest the president.

One of the Americans was identified as James J. Solages, 35, who lived in South Florida and previously worked as a security guard at the Canadian Embassy in Haiti. The other was identified as Joseph Vincent, 55.

Other suspects include 18 Colombian men, most of them former soldiers, and three Haitians.