Haitian police said they had arrested presidential security chief Jean Laguel Civil as part of an ongoing investigation into President Jovenel Moise's July 7 assassination.
Moise was killed at his home in the middle of the night by armed commandos who bypassed the president's guards without any shots fired. His wife, Martine, was seriously injured.
"I can confirm that Jean Laguel Civil was arrested Monday by police as part of the investigation into the assassination of president Jovenel Moise," police spokeswoman Marie Michelle Verrier told French news agency AFP.
Civil had already been placed in solitary confinement at a prison in Delmas, near Port-au-Prince.
Civil's attorney, Reynold Georges, said his client's arrest was politically motivated. It has not been confirmed if Civil has been charged with anything.
Four police officers and judge targeted in the investigation
Authorities on Monday also issued a warrant for Wendelle Coq Thelot, a judge for the highest court in the country, who had been fired by Moise.
Port-au-Prince commissioner Bed-Ford Claude had also ordered immigration authorities to prohibit four police officers who were responsible for Moise's security from leaving the country.
Newly appointed Prime Minister Ariel Henry has promised to bring Moise's killers to justice.
So far at least 26 people have been arrested, including 18 former Colombian soldiers.