The Serious Fraud Office (SFO) said that instead of returning thousands of pages of evidence to 59 different sources, it sent the entire batch of material to a single recipient.
The office said it had already contacted the 59 people involved and that it is "working to contact any others who may have been affected".
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Colder air slips in as the week draws to a close
The president of the world athletics body had faced repeated questions about a conflict of interests over the bid for the Eugene 2021 games.
Temperatures begin to slip away as the weekend approaches