he sixth season of Law & Order: Criminal Intent premiered on NBC September 19, 2006, and ended May 21, 2007; this was the last season to air original episodes on NBC.
This season of Law & Order: CI premiered in the NBC Tuesday 9/8c time slot as a lead-in for episodes of Law & Order: Special Victims Unit; NBC had acquired the rights to Sunday Night Football for the 2006–2007 season. For its first six airings, it faced CBS's The Unit and baseball on Fox. In late October, Fox's hit series House moved opposite L&O: CI. It was hoped that the show could maintain second position, beating the then-marginal The Unit, but that didn't occur.
The show's ratings suffered a steep drop and it regularly finished fourth in its time slot. By the end of the season, Law & Order: CI saw its lowest ratings ever on NBC, the episodes "Endgame" and "Renewal" being shifted to originally air on Monday nights.
This is the last season the original hard rock theme song was used in the opening sequence before changing to the fast-paced theme song of the now-defunct related series Law & Order: Trial by Jury - coinciding with the show's move to USA Network in Fall 2007.Overview from themoviedb.org