The person who knocked Roger's door seconds before he was murdered turned out to be his secretary. She looked all over the room until she came across the closet with his dead body. Within minutes, James was already there and started looking for evidences. His search was successful as he found a piece of hair probably belonging to the killer.
After scanning the DNA of the hair, a match was found with Kate's DNA and she was immediately remanded for further investigation.
Despite Kate's pleading to see her daughter, James took Liz along the other suspects to the police station in order to interrogate them about Roger's murder. They were forced to stay overnight for "their own safety" (even though the killer might be one of them) and Kate was allowed to see Liz for a few minutes.
But Liz never showed up. The following morning, her body was found hanged from the ceiling of one of the station's rooms.
Suspect List:
Kate
Dylan
James
Sarah
Tom
So... Who Done It?!
comment with your guess and add a reason if you like :)