"The report, which has not been published, said there were “unusual trading patterns” around 3 p.m. London time during the teleconference between the five major banks involved in the price-discovery process. The report looked at trade data from 2001 to 2013 and it noted that from 2004 there were frequent spikes in spot gold prices during the afternoon call. These spikes weren’t seen in the data prior to 2004 nor during the morning fix."
Jeffrey Christian commented on the report in this interview at PDAC, making several interesting points: