LONDON — A new report into systematic Russian doping has found that more than 1,000 Russian athletes from summer and winter sports were involved in or benefited from an organized conspiracy over a four-year period.

World Anti-Doping Agency investigator Richard McLaren released the second part of his report into allegations of state-sponsored doping, particularly involving the 2014 Winter Olympics in Sochi.

The findings confirmed and expanded on much of the evidence contained in the Canadian law professor’s first report issued in July.

Among the new specifics, the report found evidence of tampering of doping samples involving 12 Russian medalists in Sochi. The number includes athletes who won four gold medals. The names were not given.