Solution:

The youngest son went over and blew out the candle after Death left because the son said 'till the candle wick burns out', not 'till the candle burns out'.

Solution:

The wife was about to have a baby. They were driving to the hospital. The baby was born, and the wife didn't survive the birth

Solution:

1)The first bit is easy, as the first letter of each plate spells WHODUNNIT IX(A challenge to our Detective.)
2)The second bit is a little trickier, but I gave you the solution.If you read the last three letters in each plate from the bottom up and right to left you get ADVANCE EACH LETTER BY THE NUMBER SHOWN, so advance W by 5 to get B, H by 13 to get U and so on until you spell BUTLER DID IT.

Solution:

Newspaper delivery man was the murderer because of absence of Wednesday and Thursday missing newspaper.
This indicates he already know that there is no one to read it.

Solution:

We can calculate out how many days there will be for the 13th on each month if we count from the beginning of the year (January 1). Then we divide total days by 7 to get the remainders. We also need to consider the leap year. Through the whole year we had all kinds of remainders, from 0 to 6. The minimum of occurence for all the unique remainders was 1. It means that we have at least one Friday on 13th. In a regular year, the best chance you can get 3 Fridays on 13th, which are in February, March and December because the remainders of these 3 months are 2. In a leap year, the best chance you also can get 3 Fridays on 13th, which are in January, April and July because the remainders of these 3 months are 6.

Solution:

Mark Benson '?' = question MARK, so the note on the door reads 'Question Mark Crimson broke your window.'

Solution:

The forest in which the body is found was on fire. Thus a fire fighting plane was appointed on the task of putting off the fire. The plane went to the nearest lake and scooped up the water to put on the fire. Accidentally while scooping up the water, they also picked up the man swimming in the lake. Unfortunately they did not know the fact and dropped him on the fir along with the water. He died on the spot.

Solution:

The blood came from a mosquito. It bit and sucked my blood last night. It then flew and sat on the ceiling. Determined to kill it I swatted it right there and the minuscule splatter came from it only.

Solution:

This is because Adam is a hangman by profession. Apparently, his wife has been sentenced to death and he had to do it with his own hands.

Solution:

When he took the first bite of the salmon, he realized that what he ate at the island was not salmon but his friend