I've been thinking more about the case. One scenario could be that Monica was trying to blackmail Congressman Hagen again, since she didn't destroy the photos. So, he would want those photos in a bad way. I don't think he would dare kill Monica or search for them, but he would get someone else to do it. That someone could be Frank Wright, since he seems so willing to help Hagen anytime. He could've worn gloves and not leave any prints anywhere. Hagen could have other henchmen he could pay to take care of it, too.
Of course, that doesn't rule out everyone else. It's just one scenario. We have to know more about the mayor, Nicole, Rick, Craig, etc., and Candy Roberts could even be the guilty party.
I forgot how much fun this is!