Solution:

The murderer is Jack.

Christopher is the seer so exclude him.
Now, if Danny was murderer, then Garry should have been killed.
Now we know that Garry was blocked. Therefore he cannot be the murderer.
Harry can't be the killer as he was killed himself.
This leaves with Jack.

Solution:

The stranger said that he thought the room was his. If so, he must have had the keys to the room and thus he must not have knocked.

Solution:

The Bangladeshi seaman is the thief. This is because the Japanese flag cannot be identified as upside down as it is the same both ways. Thus he is just trying to escape the situation.

Solution:

The package comprises of the parachute which is tied to her back while she is diving free in the air. If she doesn't open that, she will hit the land and will die.

Solution:

The husband had booked two tickets for departure and only one for the return. The travel agent told this information to the police and they immediately came to know that he had planned the murder right from the beginning.

Solution:

The guy threw a boomerang in the air from his window. It flew away and looped around to return back with high velocity. It hit his head and he died on the spot due to the injury. This can be the only logical explanation.

Solution:

Yes, the killer is Samoa. The numbers on the calendar represents the months and the initial of every month reflects the name of the killer.
9 – September (S)
4 – April (A)
5 – May (M)
10 – October (O)
8 – August (A)

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 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.