In the act of committing a crime or other reprehensible act.

Doing something reprehensible or showing clear evidence of having done something reprehensible.

Roget 680: in the act, in the midst of, in the thick of; red-handed, in flagrante delicto [Lat.]; while one's hand is in.   

Roget 947: in flagrante delicto [Lat.]; red-handed, in the very act, with one's hand in the cookie jar.