Stockholm bishop Anders Arborelius said Wednesday in a statement posted on the diocese's website that he was aware of negationist remarks Williamson made to an investigative news programme filmed by Swedish public television SVT in November 2008 and which aired on January 21, 2009.
"I believe there were no gas chambers.... I think that 200,000 to 300,000 Jews perished in Nazi concentration camps but none of them by gas chambers," Williamson said in an interview on the Uppdrag Granskning programme.
"There was not one Jew killed by the gas chambers. It was all lies, lies, lies!," Williamson, consecrated bishop by the breakaway conservative Society of St Pius X (SSPX), added.
Arborius wrote on Wednesday: "The content of the interview with Richard Williamson ... was sent to the Vatican in November 2008, forewarning that the programme with the Holocaust denial would be broadcast on January 21, 2009."
The pope lifted Williamson's excommunication on January 24.
"We, at the diocese office in Stockholm, as we always do in matters of the Church, had forwarded the information we had about SSPX and Richard Williamson, including what we knew about the content in the interview Uppdrag Granskning had with him, to the Vatican," Arborius said.
"I want to underline that forwarding information to the Vatican is pure routine, and not something exceptional for this case," he added.
Swedish television was to broadcast a follow-up to its January programme on Wednesday, including an interview with Arborelius.
Williamson was one of four excommunicated bishops whom the pope agreed to take back into the Church in January 2009 to try to heal a split with traditionalist Roman Catholics, who rejected the Vatican's liberal reforms of the early 1960s.