The Northern Ireland Oversight Commissioner has said policing reforms are so far advanced that they are irreversible.
In a new report on the implementation of the Pattern Report recommendations, Al Hutchinson said there is nothing to stop Sinn Féin finally joining the Policing Board.
Mr Hutchinson said all that was needed was the political judgment from Sinn Féin that the time was right to act.
Mr Hutchinson said he now had full confidence in the Policing Board and the Ombudsman. "They have clearly evidenced they are up to their governance and accountability roles."
However he said in his report that the collective will of the people of Northern Ireland, and their support for the Belfast Agreement, continued to be frustrated due to "ongoing sectarian violence, paramilitary activities, organised criminality and increasingly violent assaults on the young, the elderly, racial minorities and other vulnerable groups."
There was a growing recognition in all communities that the only means of dealing with the issues effectively was a capable and effective police service and criminal justice system working in partnership with the community, he said.
"The lack of meaningful participation in the existing policing structures by all communities can only continue the cycle of violence and stability, a goal no individual or group should espouse," he said.
In a message to Sinn Fein which has, to date, refused to endorse reforms and take their places on the Policing Board and District Policing Partnerships, he said they needed to be part of the process along with everyone else.
"Virtually everything is on a good track to improvement and I don't know why they would hesitate in joining from a practical perspective," Mr Hutchinson said.