The most important part of the room is the table on the left side.
There is a list of suspects on the board above the desk.
Around the room there are simple puzzles that reveal clues.
You can tackle the clues in any order.

Clue 1

On the table with the books is a riddle to solve the three-digit code.
The answer to the puzzle is:
3 9 4
In the cabinet there is clue number 1. Simply solve the words by combining numbers and letters.

Answer:
A5 = ONE
B10 = HOTEL
C6 = OF
E3 = MURDERER
F9 = THE
G7 = EAR
A8 = RINGS
B2 = THE
D8 = AT
E6 = THEIR
G3 = LEFT

After sorting the words you get a sentence:

Answer:
“The murderer left one of the earrings at the hotel.“

Clue 2

There is a four-digit code in the cabinet to the right of the main door.
There is a paper with a number combination on the bedside table.
The paper must be tilted at the correct angle for the combination to be read.
The combination is:
6 1 8 5
In the cabinetis a decoder for text on paper.

Answer:
“Strands of dark hair were found on the victims clothing.“

Clue 3

A two-digit code is required from the second part of the first cabinet.
The code is hidden behind the image:
7 4
Match the numbers to find the words.
The first number is the row and the second number is the column.

Answer:
“I saw my reflection in the murderers glasses.“

Clue 4

It is located in the bathroom.
The door will open after the correct time has been entered on the clock.
There is a small clock on the bedside table.
So, according to this, we set the hands on the clock.
Large hour hand at 3 (III).
Small hour hand at 8 (VIII).

Next to the sink is a clue.
Just start at the bottom left corner and read RIGHT an UP.

Answer:
“I saw a very tall person running away from the hotel.“

Clue 5

Next to the sink is the key to the box on the cabinet.
Again, according to the hint, you can find out which letter has which character.

Answer:
“The murderers beard covered most of his face.“

Conclusions:

Clue 1 - The murderer wears ear rings.
Clue 2 - The murderer has dark hair.
Clue 3 - The murderer wears glasses.
Clue 4 - The murderer is tall.
Clue 5 – The murderer is a man.

So the murderer is number:
7. Jerry Sohota.

All names except 7 must be crossed out on the board.
Then the drawer in the table where the key to the main door is opened.