1
general::
In the act of committing an error or crime, red-handed. For example, They caught the burglars dead to rights with the Oriental rugs. This phrase uses to rights in the sense of "at once." [Slang; mid-1800s]
American Heritage Idioms
2
general::
Phrase(s): (bang) dead to rights
in the act; (guilty) without question. • We caught her dead to rights with the loot still on her. • There he was, bang dead to rights with the smoking gun still in his hands.
McGrawhill's American Idioms And Phrasal Verbs