The New York Times article linked in the question sets out key facts including the following ones:
Three Haitian Americans and a Colombian national have been charged in
the United States with involvement in the 2021 assassination of
President Jovenel Moïse of Haiti, the Justice Department said on
The announcement of the charges from the federal government — more
than 18 months after the murder of Mr. Moïse — outlined a sprawling
conspiracy to murder the Haitian leader and seize power, supported by
an unnamed former Haitian Supreme Court judge, Colombian mercenaries
and an illegal arms shipment from the United States.
The decision to charge the four men, who are considered to be some of
the ringleaders in the assassination plot, in the United States is an
indication of the chronic dysfunction of the Haitian justice system.
Government institutions have disintegrated after Mr. Moïse’s
assassination, and conditions in the country have worsened in recent
Three of the four men were charged with conspiracy in the murder of
Mr. Moïse: James Solages and Joseph Vincent, who are dual Haitian
American citizens, and Germán Alejandro Rivera García, a Colombian
accused of leading a group of mercenaries operating in Haiti. . . .
Dr. Christian Emmanuel Sanon, another dual Haitian American citizen,
was charged with counts related to smuggling.
Three other men had already been charged in the United States in
connection with the assassination plot.
It appears that the main basis for asserting jurisdiction is that the conspiracy to murder the President of Haiti was carried out, in part, in the United States. The Florida venue, which is where some of the smuggling allegedly occurred also supports this conclusion.
Generally speaking, under U.S. law, crimes can be prosecuted in any place where the crime is carried out or where the crime has an effect.
Strictly speaking, it shouldn't legally matter as a question of criminal procedure whether or not the perpetrators were American citizens. But that fact that all or most of the defendants are American citizens or dual American citizens is also notable. The United States probably has the constitutional authority to prosecute its citizens for crimes committed abroad, even though as a general rule, it chooses not to exercise that authority and its authority to do so as a matter of criminal procedure is a separate question.