Police believe teenagers using mace or pepper spray at a local library and grocery store sickened about two dozen people.

Surveillance tapes showed the same two teens in the Ann Arbor library branch and adjacent Kroger store.

Ann Arbor police Sgt. Jeff Connelly said the incident appears to be a prank and that investigators had not identified the two males on the tapes, The Ann Arbor News reported Friday.

Emergency crews treated people at both locations shortly after 9 p.m. Wednesday for breathing troubles, burning eyes and dizziness. Five people were treated at the University of Michigan Hospital that night and released.

Tests on the chemical substance used were inclusive Thursday.