He was speaking at a Congressional committee in Washington on Tuesday.
Dr Haass - who last year chaired all party discussions on issues such as parades, flags and dealing with the past, which did not result in an agreement - said he is confident the OTR letters "did not offer an amnesty".
He added: "I know of nothing in their content that would justify anyone walking away from the process we are discussing here today."
Earlier, a judge was appointed to head up the independent review into the scheme used by the Westminster government to deal with republican terror suspects.
In a written statement to Parliament, Northern Ireland Secretary of State Theresa Villiers confirmed that Lady Justice Hallett will conduct the review into the scheme.
Northern Ireland is often cited as a model of peace building, but this is premature. Yes, the society has come a long way from where it was two decades ago, but it still has a long ways to go before it sets an example others will want to emulate.
Details of letters sent to 'on-the-runs' detailing whether or not they were wanted by police for any crimes only emerged two weeks ago, when such a letter - sent in error - caused a trial to collapse.
John Downey, accused of carrying out the 1982 Hyde Park bombing which killed four soldiers, walked free from the Old Bailey because he had been assured that he was not a wanted man.
The 62-year-old from Co Donegal, who denied all charges against him, had received a letter in 2007.
Meanwhile the row over 'on-the-runs' appears to have overshadowed First and deputy First Minister Peter Robinson and Martin McGuinness' jobs mission to America.
UTV correspondent Tracey Magee, who is over in Washington, said the mood music between the DUP and Sinn Féin politicians has not been good.
She explained: "The mood music is absolutely awful but, no matter what is going on behind the scenes, that is not the face that they will be presenting here in Washington and the US.
"They will be smiling perhaps from the teeth out but they will be showing a united front."
The decision to grant a judge-led review was made by Prime Minister David Cameron. It came after Peter Robinson gave Westminster 24 hours to handle the crisis, saying he would quit if an independent inquiry was not launched and the letters were not rescinded.
Such a resignation would have threatened the stability of the Stormont administration, possibly sparking an early Assembly election.
But Mr Robinson welcomed the announcement that an inquiry would be granted, adding that he was happy with the terms of reference.
I am today informing the House that - following consultation with the Lord Chief Justice, Lord Thomas of Cwmgiedd - the Rt Hon Lady Justice Hallett DBE has been appointed to conduct an independent review of the administrative scheme to deal with so-called 'on-the-runs'.
NI Secretary Theresa Villiers
Sinn Féin have insisted that the letters were issued to 187 on-the-runs through a lawful process put in place by the government and that their status should not be undermined.
According to the Secretary of State, the administrative scheme is now over as far as the government is concerned.
In her statement on Tuesday, Ms Villiers added: "Lady Justice Hallett is asked to make every effort to meet the timetable of conducting the inquiry and reporting to me by the end of May 2014, for the purpose of its full publication.
"In any event, the review will conclude by the end of June 2014."
Lady Justice Hallett was previously appointed as the coroner who presided over the inquests into those killed in the 7/7 terror attacks in London.