PRINCETON (AP) — Princeton University says it found no evidence its researchers mistreated a monkey that they put into a ferret exercise ball and had it roll on the floor for 13 minutes.

McCosh Court at Princeton University (Mahlon Lovett, Princeton University, Office of Communications)

The university conducted an internal investigation after People for the Ethical Treatment of Animals filed complaints with federal officials in June.

The Times of Trenton reports the university on Monday released the results in which it found no evidence of mistreatment. But the school did say the experiment was not preapproved, as required for all animal experiments, and lab staff must be retrained.

PETA had claimed lab staff placed the monkey in the ball for amusement. But Princeton says it was done to explore its use by marmosets.

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