Help:Can they nail my brother for trespassing? need a quick, correct answer?

My younger brother (18) went to visit an abandoned asylum and cops came. Its so common among these kids, i don't know why they bother, but anyway, they ran and a few were caught. they gave my brother's name and the cops just called to say he has to turn himself in my 6am. Can they legitimately arrest him if they didn't see him there?