Posted by James Briggs on March 10, 2008 at 11:26:
In Reply to: Dead to rights posted by Smokey Stover on March 09, 2008 at 19:26:
: : I found a query posted in 2002 when I went looking for the origin of "Dead to rights." Nobody was able to help. I'm wondering: has anyone come up with an answer in the five years since?
: This is a slang phrase originating in the U.S., combining two common words used idiomatically. "Dead" in this case means completely or absolutely, as in "dead broke," or "dead on." "To rights" or "to right" has a very old history, and is related to "make right," or "put right," put in, or restore to, proper condition or order. It has often been used in connection with one's personal health, as in, "a little tea and then a night's sleep will put me to rights."
: "Dead to rights" is seen from the 19th century on, and is used mostly, I believe, as a synonym for red-handed or in the act, or at least with positive evidence of guilt, as in "I caught him dead to rights," According to the OED it can also be used to mean "completely, certainly."
The Archive contains several discussions about this, and the related 'bang/ed to rights'. See link