Police in Haiti arrested a man on Sunday who is accused of being a key figure in the plot to kill President Jovenel Moise.
The 63-year-old suspect is a Haitian national living in the US state of Florida. He identified himself as a doctor, and had accused Haitian leaders of corruption in videos on YouTube.
Suspect in touch with assailants
The man is suspected of working with a group of men who plotted and carried out Moise's assassination, said the head of Haitian national police, Leon Charles.
"This is an individual who entered Haiti on a private plane with political objectives," said Charles.
He added that the suspect had entered Haiti along with several of the alleged gunmen in the attack, but the initial plan was only to arrest Moise and seize the presidency.
Authorities said after the killing, one of the gunmen called the 63-year-old suspect. He had allegedly hired a private Venezuelan security firm based in Florida for protection.
The doctor is the third US resident of Haitian origin to be detained as a suspect in the assassination probe.
US assisting with investigation
Members of the FBI, the US State Department, Justice Department, National Security Council and Department of Homeland Security arrived in Haiti to assist with the investigation.
The delegation met with interim Prime Minister Claude Joseph, whose appointment has been questioned by Joseph Lambert, president of the Haitian Senate.
"I met with the US delegation and together we welcomed the resolution of the Senate that chose me as interim president of the Republic," Lambert said in a tweet.
The next elections in Haiti are scheduled for September.
Dozens of people are suspected of involvement in the attack on Moise's residence in Port-au-Prince, with 21 people currently detained. Moise's wife was also wounded in the attack, which took place early on Wednesday.
Police have said 26 Colombian nationals are suspected were involved in the murder — 18 of whom are in detention.