As Blue Velvet nears the final scenes, Jeffery enters Dorothy's apartment and sees that Vallens is dead and Gordon has been inflicted with some type of grisly brain trauma. Vallens had presumably been held prisoner at 'This is It', and Gordon had been either at home or on patrol.
The question is...
What was the killer's rationale for moving the victims to Dorothy's apartment? In fact, who was the killer? If it was Frank as all logic suggests, the sequence of actions would have been
- move the victims to Dorothy's apartment;
- kill Vallens
- perform brain damage on Gordon
- leave the apartment
- change clothes into the 'well dressed man' outfit
- return to the apartment with the briefcase expecting that no one else than the victims would be there...
...and to do what? It doesn't make sense.
How to unsnarl this sequence of events into something coherent?