He also clarified that some media reports that he had broken up the donation into smaller amounts were incorrect.
"The funds, before it entered National Party accounts, came in in amounts smaller than the $15,000 disclosure threshold. The $100,000 donation was offered directly by the donor to Bridges.
It was not until a later time that he was asked by Bridges to make contact with the donor.
Ross said he would be happy to co-operate with the SFO in its investigation.
"Every time that I've been told that I was wrong or baseless, I've come up with some evidence or some information. This just shows that there are some serious issues there around donations in the National Party that should be investigated properly."
In response to Bridges' comments today that it was the party, not him who faced questions, Ross said Bridges had to at some point realise he was the party leader.
"I was not there on the 21st of May. [National Party president] Peter Goodfellow was not there on the 21st of May. The donation was made to the leader of the National Party and his involvement, he has to answer," Ross said.
At the time, the party was trying to raise money for attack ads and Bridges had been excited about the big donation, he said.
"I don't have a recording of that but he was at pains to point out to me … that it would be unhelpful for the donation to made public. Anything over $15,000 has to be declared.
So when the donation came in, when the $100,000 amount came in, it was in separate parcels below $15,000."
He said the names and addresses tagged to the donations were eventually provided to the National Party. Ross said he was unaware whether questions about the names and addresses from National Party general manager Greg Hamilton were ever resolved.
"But it was very clear that it was $100,000 offered to Simon Bridges on the 21st of May."
