Anyone here likes Riddles? Mysteries? Better yet, Murder Mysteries?

Don't answer if you already seen this scenario in a book, anime, or tv show. Feel free to PM me the answer though or gloat / discuss it. Feel free to post your owns, better yet if you thought them up yourself.

ALL ANSWERS MUST BE WRITTEN IN WHITE WITH A SPOILER WARNING ONTOP OF IT!

Mystery 1 Chained Locked Room.
Blood is found seeping through an apartment door, police are called and the landlord gives the detectives the master key. The door barely opens a creek, and there's a chain still on, so they come through the fire escape, window is locked and barred, which the cops have to break off and break the glass to get inside.

Inside they find two bodies. Fallen against the door is the wife. In the bathroom bedroom, they find the husband, on the floor. Both are dead. Husband died due to being stabbed in the throat. The wife died the same way. There murder weapon is no where in the apartment, and the apartment is completely locked. The keys to the apartment was found on the table, only husband and wife fingerprints found.

How did both the husband and wife die? To recount.
- Husband body was in the bedroom.
- Wifes body was slumped against the front door.
- Windows were locked from the inside and barred, had to be broken off to remove.
- Front door was both locked and had a chain on.
- No murder weapon in the apartment.

Hints below (3 hints total)
1 - No forced entree.
2 - Apartment door auto locks upon closing.
3 - Conspiracy.

Disclaimer: My solution does not necessary extend to being the only possible solution.