"Mercenaries came to the president's house, they tortured him and they killed him," Joseph said. "We captured about 20 of them. They are currently in custody. And we believe, we staunchly believe, that justice will be provided to the President Jovenel Moise… We do have the right people [in custody].”
At around 1 a.m. local time on Wednesday, an armed group stormed Moise’s residence and shot and killed the head of state. The group claimed to be U.S. Drug Enforcement Administration agents during the raid, according to Haitian Ambassador to the U.S. Bocchit Edmond, which both the Haitian and U.S. governments have denied.
In the interview on Friday, Joseph said his main focus was to bring justice to Moise’s family as the leadership crisis threatens to bring more hardship and chaos to one of the poorest countries in the world.
Joseph, who appeared emotional in the interview, said he was "shocked" at the manner of Moise’s death.
On Saturday, an audio message from Martine Moise, the first lady of Haiti, who was wounded in the attack and airlifted to Florida to receive treatment, was released from her official Twitter account. A Haitian official told ABC News that it was authentic.
"This great act of murder makes me and my children cry, and I know you are crying too," she said. "This act has no name, because it must be a crime out of bounds to assassinate a president like Jovenel Moise without giving him the opportunity to utter a word."
At least 17 suspects have been arrested in connection with the assassination, including two U.S. citizens, identified by the authorities as James Solages, 35, and Joseph Vincent, 55.
Haitian Judge Clement Noel, who is close to the case and said he had interviewed the pair, told ABC News they claimed to be working as translators for the group and denied being mercenaries. According to Noel, Solages said he found the job on the internet and that they were supposed to arrest Moise rather than kill him.
"We are certainly aware of the arrest of the two U.S. citizens who are in Haiti and continue to closely monitor the situation," U.S. State Department deputy spokesperson Jalina Porter said.
Fifteen of those arrested were Colombian nationals, some of whom are believed to have military backgrounds, according to the Colombian authorities. Two Colombian nationals were killed in a shootout in Port-au-Prince on Wednesday, Noel confirmed.
Letters viewed by ABC News show the Haitian government asking both Secretary of State Antony Blinken and the United Nations to send troops to help stabilize the the turbulent Caribbean nation and support national police. The troops were also requested to protect key infrastructure, including the airport, ports and gas terminals, as well as to help maintain electoral security.
On Saturday, a senior administration official told ABC News that "there are currently no plans to send U.S. military assistance to Haiti."
The White House said Friday that FBI and Department of Homeland Security officials would be sent to Haiti to assist with the investigation into the assassination.
While Haiti's streets remain relatively quiet, Joseph’s authority has been contested by another candidate for the position of prime minister, Ariel Henry, who was scheduled to take over before the assassination this week. Henry and his supporters have questioned Joseph’s legitimacy.
Prior to the assassination, Moise’s opponents claimed the former president had overstayed his time in power, while the U.S. and U.N. both backed his claim that his term was scheduled to end in February 2022.
State Department spokesperson Ned Price said that the U.S. would continue to work with Joseph since he is the incumbent, saying that U.S. officials had also been in contact with Henry, urging calm.
Joseph Lambert, the president of Haiti’s Senate, has positioned himself as the next interim president, though it remains to be seen who he would back him. Eight sitting senators have so far signed a memorandum in support of Lambert’s appointment, but the situation is constitutionally unclear.
Asked about the political power struggle, Joseph said that his main focus was on the investigation into Moise’s assassination.
"I don’t know if there is a power struggle. I’m not paying attention to whether or not there is a power struggle. I’m paying attention to giving justice to President Jovenel Moise... but I was interim prime minister. After the tragic death of Jovenel Moise I had to take charge and I did.”
ABC News' Marcus Moore, Conor Finnegan, Sarah Kolinovsky and Kirit Radia contributed to this report.