Anyone who has been the victim of crime should co-operate with the police, Gerry Adams has said.
Gerry Adams said the victims of crime should go to the police
The Sinn Fein leader said that he still had concerns about collusion, but people should help police get rapists off the streets.
At a weekend meeting Sinn Fein members voted to back the Police Service of Northern Ireland (PSNI).
Mr Adams said the PSNI had to earn trust "by being professional, non partisan and a civic policing service".
"Let there be no doubt about this," he said.
"If some unfortunate person is the victim of a rape, if those despicable elements who are going around terrorising old people in their homes continue, and if death riders continue to mow down people, if that happens, Sinn Fein will be encouraging people to work and co-operate with police to take these people off the streets.
"The communities we represent have a right to a policing service."
Earlier, Northern Ireland Secretary Peter Hain said he is convinced DUP leader Ian Paisley is ready to be first minister on 26 March.
Mr Hain was speaking after he had what he called "a successful meeting" with the DUP leader Ian Paisley on Monday.
He warned that all the parties had to fulfill their obligations before the assembly could be restored.
Mr Hain said it would be "an absolute tragedy" if devolution didn't go ahead.
"I am convinced that Ian Paisley is ready to be first minister on 26 March, as I am convinced Sinn Fein are going to deliver practically on the ground in what they have promised to do in policing and support for the rule of law," he said.
"It is worth just saying that we have never ever been in this position before and it would be an absolute tragedy if, somehow, both the DUP and Sinn Fein contrived to find a reason not to do the deal and have devolution on the 26 March."
Earlier on Monday, the British and Irish prime ministers welcomed Sinn Fein's decision to back policing in Northern Ireland.
The motion to support the PSNI was backed by 90% of the 900 members who voted at the party's conference (ard fheis) in Dublin on Sunday.
Tony Blair's spokesman said the ballot was an "historic decision", while Bertie Ahern said it was a "landmark".
But DUP MP Nigel Dodds said he doubted Sinn Fein could prove its support by the 27 March deadline to revive devolution.
"If they are going to stick to this policy then there will certainly be no delivery before 26 March and therefore there can't be the time for the delivery or the testing," he said.
"Therefore I think there are very, very serious problems - let Sinn Fein get on with doing what other parties have already done."
On Monday, Sinn Fein's chief negotiator Martin McGuinness said he hoped the DUP would respond positively following the party's decision to support the police and the rule of law.
Mr McGuinness said republicans were aware of the problems within their communities.
"People recognise that this is an area that needs to be dealt with.
"I experienced this myself in my own constituency where a 77-year-old man was murdered and, in the same incident, his 75-year-old sister was raped and thrown down the stairs.
"I think that we do need to be liberated to move forward to ensure that those who are responsible for these heinous deeds are apprehended and brought to justice."
Northern Ireland Secretary Peter Hain said people need to know that "if there's a rape or a burglary or a drunken yob runs riot in a neighbourhood, local republicans are co-operating with the police".
"I think that we're moving in that direction and the important thing is that we've never been at this point before," he said.
The decision gives Sinn Fein's ruling executive the authority to declare its support for the PSNI and the criminal justice system when devolution is restored and policing and justice powers are transferred to the Northern Ireland Assembly.
Mr Ahern said the move opened the way to Northern Ireland power-sharing.
Chief Constable Sir Hugh Orde also welcomed the result of the ballot.
Mr Blair and Mr Ahern have identified Sinn Fein support for the PSNI as crucial to persuading the DUP to share power in a devolved government with Sinn Fein by 26 March.
If an election does not occur, Stormont will be dissolved indefinitely.