Solution:

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

Solution:

The thief turned out to be Anthony, who cunningly concealed the watch inside a bucket.

Solution:

The pregnant lady.

The detective Byomkesh Bakshi noticed that the pregnant women look 6-7 months pregnant in January, May, and even in July. So that pregnant lady is the thief we are looking for and must be faking her pregnancy.

Solution:

The Lady sitting in the chair has the detector attached to the back of her blouse.

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:

The thief is the Pakistani guy. It is because the flag of Japan looks same when upside down and no one can tell if it is upside down. So, he was telling a lie.

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.