"They looked at everything: change of addresses, illegal immigrants, ballot harvesting, people voting twice, machines being tampered with, ballots that were sent to vacant addresses that were returned and voted," one person familiar with the work told the newspaper.
About a dozen people from the Berkeley Research Group, including econometricians, worked at the report in the final weeks of 2020, before the January 6 US Capitol riot, but none of the findings were presented to the public or in court, media said on Saturday.
Four people familiar with the matter told the newspaper that the researchers could not find indisputable proof that Trump was the winner of the election, although they believed that there were voting anomalies and unusual data patterns in several states, as well as some instances in which "laws may have been skirted."
Trump has repeatedly said he considered the results of the 2020 presidential election in several US states to be fraudulent, robbing him of election victory, and has been a subject of a political witch hunt as a result of his efforts to prove election and voter fraud.