"The survivors who are affected, or believe they have been affected by it because they have been notified of which files were on the computer — they have contacted us," Sinclair said in an interview with CBC News Network's Power & Politics on Friday.
CBC News reported on Thursday that Canada's privacy watchdog has been asked to look into a possible breach of personal information belonging to residential school survivors, after an adjudicator working for the agency handling their compensation claims filed a police report citing blackmail.
The Indian Residential Schools Adjudication Secretariat is the administrative body that manages the claims made by residential school survivors.
Survivors can seek compensation for abuse they have suffered in residential schools through an independent assessment process (IAP) managed by the agency.
"They have spoken to us about their concerns and what we have committed to them to do is to follow up with the investigation officials as well as the IAP officials, just to determine what steps are going to be taken to protect the privacy issues that they're raising with us," Sinclair told guest host Rosemary Barton.
Sinclair said it was his understanding that the personal information included medical records and case summaries detailing the abuse the survivors endured.
"Medical records are inherently private. But in addition to that, it would probably include residential school experiences and other related matters to that."
"That causes concern among survivors because they were promised confidentiality when they were interviewed by the IAP staff," Sinclair said.
"And to now think that confidentiality may have been meaningless if the documents are in the hands of other people would be a grave concern to them emotionally."
Privacy watchdog asked to investigate
NDP MP Charlie Angus, who represents a northern Ontario riding where a residential school once operated, asked the Office of the Privacy Commissioner to investigate the matter in a letter dated March 27.
"I respectfully request that you undertake an investigation of this data breach, how and when it occurred, and the practices of both the IAP and Aboriginal Affairs and Northern Development Canada in responding to this breach — and make recommendations as to how their practices can be improved," Angus said in his letter to the interim federal privacy commissioner Chantal Bernier.
Angus also wrote a second letter to Daniel Shapiro, the chief adjudicator at the Indian Residential Schools Adjudication Secretariat, asking him to make public the details of the incident.
"I have no desire to point the finger at any individual employee," Angus said in the letter to Shapiro.
"However, the larger issue of protocols for protecting personal data must be considered of paramount importance. It is important to reassure the survivors and the public that every measure was taken and is taken to address this potentially damaging breach."
A spokesperson for Shapiro told CBC News on Wednesday that "an individual contacted the secretariat earlier this month" claiming to have information relating to claims made by residential school survivors.
"The adjudicator has made a report to the police, and indicated that blackmail was involved," Michael Tansey, a senior communications officer with the agency, said in an email to CBC News.
He also said the agency had yet to determine whether the individual who contacted them actually possessed any confidential information or was bluffing.
Tansey said the secretariat informed the Department of Aboriginal Affairs "shortly after" the agency became aware of it, and that it referred the matter to the privacy watchdog "this week."
The office for the federal privacy commissioner confirmed to CBC News on Wednesday that the matter had been reported to it by the Department of Aboriginal Affairs on Monday.
It is unclear how much time elapsed between the time that the incident occurred "earlier this month," as Tansey said and last Monday, when the matter was referred to the privacy watchdog.
Who is responsible?
Aboriginal Affairs Minister Bernard Valcourt said on Tuesday that the secretariat is an independent organization for which his department "is not responsible."
But Angus, who believes the claims process does fall under the Department of Aboriginal Affairs, has asked the privacy watchdog to clarify who would be responsible for the data which may have been lost or stolen.
This is not the first time there has been a possible privacy breach of personal information belonging to residential school survivors.
The office of the privacy commissioner said it was notified of a separate incident in 2013, while the agency said a possible breach was identified in 2012.
It is unclear whether those two incidents are related to this month's event.
The secretariat is an independent, quasi-judicial tribunal established in 2007 under the Indian Residential Schools Settlement Agreement.
Sinclair said he did not have any more information on the incident other than what the residential school survivors told him. "Even if we had an opportunity to ask questions about it, we would probably respect the investigation that is now ongoing and not pursue it at this point."
Sinclair was in Edmonton for the final hearings of the Truth and Reconciliation Commission.
The commission will have to submit a final report by June 30, 2015, when its mandate comes to an end.