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.

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.

(Copyright 2014 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed)