The D.C. police get involved and begin looking for the killer. They quickly realize that a robbery was also happening at the time of death. They only have a handful of suspects who could have pulled off such a complicated job. Luther comes to their mind as a suspect. The head detective Seth (Ed Harris), doesn't believe that Luther could commit murder. He pegs him for the robbery but not the murder. Once Luther knows that they've got him made for the job, he takes it upon himself to hid out and hunt for the killer. He knows who it is, he just has to catch them and get them to incriminate themselves.
When the killer starts to go after Luther's daughter that's when he draws the line in the sand and now it's every man for themselves.
Watch this great Clint Eastwood movie. It's a seat gripper all the way to the end.