The police hold Christine as a "material witness" to avoid the obligation to release her after 48 hours. This is indeed still a thing, even though this controversial use of the material witness statute is under judicial review: since September 11, 2001, the U.S. has used the material witness statute to detain suspects without charge for indefinite periods of time, often under the rubric of securing grand-jury testimony.
When Dexter communicates on the CB radio he uses the call sign "Little Chopper" which is rather fitting for a guy who chops up bodies as a hobby.
Included in the DVD set "Most Shocking Episodes".