Solution:

1. Check the list on the tree, It's a list of 6 people.
2. A spider has woven a web near the tent. This means they must have been staying for a few days at least.
3. Two men are having lunch.
The third one is measuring the depth of the river.
The fourth one is fishing.

Solution:

No hole for the key.

Solution:

Tire marks of right's man car are matching.

Solution:

Wristwatches

Most of us must have assumed the answer to be a ring in the wrong finger but that's not the case as it's a normal ring. The error is in the watch. Wristwatches are manufactured with the adjustment pin always on the right side.

Solution:

There are 7 people.

Solution:

The pic is from 70's Era and modern cell phone was not around at that time.

Solution:

Check a lipstick mark on the glass of the kitchen.

Solution:

The thief is encircled.

Solution:

Change your point of view and look the picture upside down.

Solution:

The boy in the center. He doesn't have any shadow.