Solution:

The boy on the right is the one. The piece of his shirt is with the deceased girl, as indicated.

Solution:

I have three theories based on which it can be either Murder, Suicide, or Accident.

Case1 : Its a Murder
Reason1: If it's suicide then a person must have waited for the Cigarette to end.
Reason2: Blood is spattered on the right side and the pistol is also on the right side. which seems pistol is planted at the end.

Case2 : Its a Suicide
Reason1. The lamp was switched off and glasses were removed which indicates she done writing(probably suicide note). The murderer does not care about switching off glasses or removing glasses.
Reason2: The blood was just on the wall at the height of a person. If it's a murder the blood must have been scattering around.
Reason3: Burning cigarette and alcohol indicated depression level which often is the reason for suicide.

Case3 : Its a Accident
It's must be an accident. The girl was writing using the pen and suddenly she heard a sound. She must have a gun for safety which she takes out of the security. As a preventive measure, she switched off the light so that she can't be seen in the dark. Also removed the glasses as they are of no use in the dark. After a while, she realized that it's just a sound. So to calm her down she drinks and also lights a cigarette. suddenly she slipped and try to hold stool but failed and forced her head into the wall and died.

Solution:

Upon reaching each room, he found out that the window facing the dead body was closed. He had to open the window himself. This tells that there was somebody else with him who closed the window. If he would have committed suicide, at least one window would have been open.

Solution:

In this picture, he saw another man. If you try to look near the right end of the picture, you will find a fan. Go down for the phone that is plugged on charge. Go further down and you will find a man's face. An eye is particularly visible. The man was hiding behind the bed when the husband arrived in her room. This made him believe that his wife was cheating on him.

Solution:

If the man killed himself, he would not have been able to rewind the cassette. Thus it is clear someone else killed him.

Solution:

Kid1, he was left with one rock.

Solution:

A) The caretaker

There is no blood, but the woman is dead. Her mouth and eyes are also open. She was put to death using a non-bleeding technique.

The chef with the knives and the waitress with the gun couldn't have murdered the woman.

Therefore, the murderer who used a rope to strangle the victim is the caretaker.

Solution:

Rasmas is lying, how can he be so well-shaven after being alone in the woods for a week?

Solution:

The death was ruled a suicide.

Solution:

Murder.

Explanation:
1. There are signs of the struggle in the room as the clock is broken.

2. Two water glasses in the room indicate the presence of two people which also suggest that the killer is known to the victim.

3. There are a book and a pen on the bed which indicates that the dead person was reading and a suicide note was written from another pen which seems to be planted.

4. The man crutches are too far from the man.