He investigated the genocide and ran the legal office of the UN International Criminal Tribunal in Rwanda from 1995 until 1999.
"It was the same thing. There are dozens and dozens of incidents, where you have the same pattern. It was systematically done," he said.
Cote's comments came in advance of the official release next month of a 600-page UN report co-authored by him on atrocities committed in the central African nation.
It is a nightmarish inventory of murder, rape and looting that took place in the DRC from 1993 until 2003 as it was torn apart by more than half a dozen plundering armies.
The report's most damaging element says that Rwandan Tutsi commanders and their rebel allies may have committed genocide.
"The systematic and widespread attacks described in this report ... reveal a number of damning elements that, if they were proven before a competent court, could be classified as crimes of genocide," stated the probe.
Rwanda dismissed the report as malicious and ridiculous, accusing the UN of seeking to bury its own failings.
"It is immoral and unacceptable that the UN, an organisation that failed outright to prevent genocide in Rwanda ... now accuses the army that stopped the genocide of committing atrocities in the Congo," Ben Rutsinga, the Rwandan government spokesman, said.
France's Le Monde newspaper said Rwanda had threatened to withdraw peacekeepers from Sudan's Darfur region over the charges.
The UN has said the leaked report was only a draft version and experts say diplomats are debating whether to include the genocide accusation in the final copy of the document.
Cote's probe, a draft of which was obtained by the AFP news agency, is silent on the death toll though it found evidence suggesting tens of thousands of Hutus had been killed.
UN and other aid agencies said in the 1990s that 200,000 Hutus were unaccounted for.
The possibility of genocide forms only a part of the UN report.