At the time, the charity only referred to it as "serious misconduct".
Late on Friday, the Department for International Development (DFID) also said it was reviewing its relationship with the UK-based charity, to which it gave almost £32 million (36 million euros/$44 million) a year ago.
Oxfam has denied that they took part in any coverup thought according to reports they did not let the Haitian government what was happening which meant they were unable to take legal action against the employees involved.
The source added staff members did not speak up for fear this might reduce donations to the most vulnerable at a time when funding is under pressure.
"But I don't think it was in anyone's best interest to be describing the details of the behavior in a way that was actually going to draw extreme attention to it when what we wanted to do was get on and deliver an aid program".
In addition to the country director, six other workers left the charity after its internal investigation: Two resigned and four were fired for offenses such as "use of prostitutes on Oxfam property" and possession of pornography, the Times reported.
Some of Oxfam's staff allegedly hired prostitutes while in Haiti trying to help the country recover from the 2010 natural disaster.
Mr Van Hauwermeiren went on to work elsewhere in the sector.
Save The Children said all 31 abuse allegations took place in foreign countries and that 16 people had been dismissed as a result.
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"There are some actions I'm looking for them taking now".
Public confidence in the way Britain's foreign aid money is spent has been undermined by a number of scandals.
Many aid agencies have procedures covering safeguarding, whistleblowing and misconduct - collectively, we must work harder to ensure they are fit for goal, to root out improper conduct. It is not clear whether anyone from DFID made any attempt to investigate what the "nature of the allegations" was.
The UK now spends £13bn on aid each year and there have always been calls from some Conservative MPs for cuts to this budget.
It said Oxfam's leaders had "showed a lack of judgment" in their handling of the matter and their level of openness with the government and commission.
Among the provisions is a pledge to work with other aid organizations to overcome "the legal difficulties which have so far prevented us from sharing intelligence" with other aid agencies regarding staff members previously accused of misconduct. We are committed to ensuring that such behaviour is not tolerated either within our organisation or across the aid sector.
Yesterday International Development secretary Penny Mordaunt vowed to axe funding to Oxfam and "any other organisation that has safeguarding issues".
The former International Development secretary Priti Patel told the BBC: 'There are no databases of these predatory paedophiles that exist and we need them ... to stop this disgusting and corrosive culture of the revolving door in aid agencies'.
She said Oxfam often worked in very hard locations "where the rule of law isn't going on".