Trying to find the name of the murder/mystery movie: -

Female Cop/detective tries to uncover a series of murders with the help of her new police partner. As it turned out, after going back to her partner's home town and finding out stuffs, it turned out, he was the killer all along.

Thanks for all the help.

Sounds like an Ashley Judd flick

Twisted?

Amazon.com: Twisted (2004) (Dol) [VHS]: Ashley Judd, Samuel L. Jackson, Andy Garcia, David Strathairn, Russell Wong, Camryn Manheim, Mark Pellegrino, Titus Welliver, D.W. Moffett, Richard T. Jones, Leland Orser, James Oliver Bullock, William Hall (II