The President of the Equestrian Federation of Ireland, Avril Doyle, has said that a number of documents were removed during a break-in at the federation's offices at Kill, Co Kildare, overnight.
She said she was extremely annoyed at the robbery, and while she could guess in whose interest it would be to have the documents, she would not comment on who might be involved.
Gardaí investigating the break-in are trying to establish if it is linked to the doping controversy over Olympic showjumping medallist Cian O'Connor.
Earlier, Ms Doyle had described the development as sinister.
She said the front door of the office at Kill had been forced open, and it appeared that a filing cabinet had been disturbed.
It follows the disappearance of the second urine sample taken from Mr O'Connor's Olympic mount, Waterford Crystal.
Mr O'Connor had demanded that tests be carried out on the B sample after an earlier one had shown that his horse had traces of a sedative in his system while competing in the Athens Games earlier this year.
Drugs in A sample should not be used: FEI
RTÉ News has learned that the drugs that were found in the A samples of Mr O'Connor's horses, ABC Landliebe and Waterford Crystal, should not have been used in horses.
The Swiss-based governing equestrian body, the FEI, has said that any use of the drugs concerned would be considered as an attempt to manipulate performance by medication.
RTÉ News earlier established that the substances found in the A sample were Zuclopenthixol (clopixol), Fluphenazine, Guanabenz and Reserpine.
However, Mr O'Connor's solicitor, Andrew Coonan, told RTÉ News that they do not accept the finding of the A sample in relation to Waterford Crystal.
Mr O'Connor has continuously protested his innocence in the matter.
Controversy damaging showjumping: Kuerten
A member of the Irish Olympic Showjumping team has described the Cian O'Connor controversy as extremely damaging to the sport.
Jessica Kuerten said that it was up to the Equestrian Federation and Cian O'Connor to hold a press conference to explain the situation.
Separately, senior figures in showjumping have called for an inquiry into the second sample's disappearance.
They include his former Olympic trainer Eddie Macken and two of his teammates at the Games, Marian Hughes and Kevin Babington.
Three European police forces are co-operating in the investigation into the theft of the sample.
The governing body of the sport, the FEI, said the sample was stolen in Cambridgeshire in England as it was being transported to the horse racing forensic laboratories there from Paris on 21 October.
British police are working with their Swiss and French counterparts to try to establish who stole the sample.