Solution:

It is simple. The sheriff never told him where the crime scene was. But still he reached at the right place. This points towards the fact that he knew it already and that he is the killer himself.

Solution:

At every floor, the detective had to open the window himself. If the man had committed suicide, then at least one of the windows must have been open. A person who is committing suicide won’t close the window behind him. Thus he knows that someone pushed him off the edge and closed the window afterwards.

Solution:

This is more of a philosophical question than being a riddle or a puzzle. The action of Brian directly led to the result which is the death of Chris. Thus he murdered Chris. In a sense, Chris died due to the lack of water. It is the circumstances that ultimately led to his death.

Solution:

The wife booked a two way ticket for herself and booked a one way ticket for her husband.

Solution:

It is possible that the man was a deep sea diver. Such divers must wear a pressurized suit to withstand the pressure in the depths of the sea. If it tears down accidentally, the person will die. But for a short period of time, the breathing apparatus can keep him alive.

Solution:

The code word is TIE.

Let us assume that the word is MOD. Now if you are told one character of this word, you would not be able to identify the number of vowels in the word. For example if you are told M, then the word can be MOD or AIM but they both have different number of vowels. If you are told about O, then there are two words MOD and OAT which again have different number of vowels. If you are told about D, there are two words again MOD and DUE which have different numbers of vowels again.

In such manner, all the words that have M, O or D in them can be excluded. Then only word that remains is TIE.
If you are told about T, there are two words OAT and TIE which both have two vowels.
If you are told about I, there are two words AIM and TIE which both have two vowels.
If you are told about E, there are two words DUE and TIE which both have two vowels.

Thus TIE is the code word.

Solution:

The dead man used an ice knife to commit suicide. The ice held the knife pointing upwards as he dropped on the chair with his back facing the knife. Later, the ice melted leaving moisture around the body.

Solution:

It is quite possible. The poison was not on the drink but in the middle of ice cubes. The first one drank immediately and thus the poison could not reach his body while when the other drank after half an hour, the ice cubes had melted. Thus he died.

Solution:

The guy was killed a long ago, but he could not realize it till he reached his room. No need to be confused. Actually the killer has somehow inserted an extremely fine and thin incision blade in the belt of the guy. The guy did not feel anything at the moment as it was extremely fine. But when he was changing his clothes and took of his pant, the incision knife that was in his body, came out stuck to the belt cutting him very finely on the insides. That is the reason there was so much blood loss that he died and it was so fine that it was not visible to the naked eyes.

Solution:

When you were inside the shed, the murderer replaced the lock with his own one that was identical to your original lock. When you locked the store room, you did not require a key and there was nothing abnormal for you. When you left, the murderer opened the lock with his key, planted the dead body inside and replaced the lock again putting the original lock in the place. He then closed it without any problem.