Solution:

Oscaru and Austin.

Explanation:
The Chemist hide the name using periodic table as shown in below picture
76-20-44 => Os(76) + Ca(20) + Ru(44)
79-16-22-7=> Au(79) + S(16) + Ti(22) + N(7)

Solution:

The man with the cast

Explanation:
Reason-1: The blood strain is on the left side of the dead man which means the killer is most likely a left-handed. The cashier and man with the cashier are both right-handed.

Reason-2: Why will a man with the cast go for buying shirts/coat? Seems suspicious.

Reason-3: The man with the cast must be carrying the weapon inside the cast.

Solution:

It's a Murder.

Explanation:
1. There is a sign of the struggle in the room.

2. In case of suicide, bullet wound is generally on the head but here the wound is on the chest.

3. The dead man is left handed as all his the stuff like phone pens are on the left side but the gun is on the right-hand side (must be planted).

Solution:

Costa

Explanation:
Costa brings the dagger made of ice in the thermos so it won't melt. He killed the Michy with the dagger and then the dagger melts with time.

Solution:

Ruppell's vulture generally found on high altitude and Mr. smith was on the plane. The vulture hit the plane and the plane got crashed.

Solution:

Dean Winchester shoots himself in the mirror.

Solution:

The dead guy is Superman. He died because he was exposed to a Kryptonian rock.

Solution:

Tennis Player is the only man there and peter is the name of a man.

Solution:

The police officer knows the story was not true since Vasco was shot from back and he was injured only in the stomach.

Solution:

McLaughlin