Colombia's President Iván Duque says some of the Colombian suspects in the assassination of Haitian President Jovenel Moïse had "detailed knowledge" of the plan to kill the leader.
Mr Moïse was shot dead last week in his home and his wife injured.
Haitian police say a group of mercenaries mainly made up of Colombian ex-soldiers killed Mr Moïse.
Mr Duque said most of the Colombians had been duped as they were told they would work as bodyguards in Haiti.
But there was a smaller group among them with detailed knowledge of the operation, he told Colombia's FM radio.
Of the 28 men alleged to have made up the commando which killed Mr Moïse, all but two were Colombians while the other two were US citizens of Haitian descent.
The US defence department has since revealed that some of the Colombians received military training in the US while they were in the Colombian army.
A Drug Enforcement Administration (DEA) source also told Reuters news agency that one of the Haitian-American suspects was a "confidential source" for the DEA.
Haitian officials said that the assailants had disguised themselves as DEA agents.
In a video purportedly shot shortly before the attack outside the president's residence a man can be heard shouting in English "DEA operation, everybody stay down!".
The Haitian police has also arrested a Haitian doctor, Christian Emmanuel Sanon, whom they described as a "key suspect" in the assassination.
The 63-year-old Florida resident arrived in Haiti on a private jet in June and police said they found a DEA cap as well as weapons and ammunition in his possession.
A New York Times (NYT) investigation suggests that Mr Sanon and a number of other suspects met to discuss what would happen to Haiti once Mr Moïse was no longer in power.
But a man present at some of the meetings told the NYT that Mr Moïse's assassination was not discussed.
Police are still searching for what they call the "mastermind" behind the plot.
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