Garcia told the FIFA congress in Sao Paulo yesterday that he was prepared to use the documents printed by Britain's Sunday Times in his probe, shooting down media "assertions" that he may ignore them.
The explosive documents have cast new doubt on Qatar's World Cup, with major sponsors urging a thorough investigation and some FIFA delegates calling for a re-vote if corruption is proved.
"The vast majority of that material has been available to us for some time, since well before the recent wave of newspaper reports," Garcia said.
The British newspaper has published a series of reports based on millions of leaked emails and documents which claim widespread bribery orchestrated by former Asian football chief Mohammed bin Hammam.
Garcia said investigators had combed through the newspaper's reports and all the documents attached. He said they had gone to "what appears to be the original source" and should have access the entire cache of data.