disinfectant spray bottle Riddles

You are distributing vegetable oil. There are 21 bottles in total out of which 7 are full, 7 half empty and 7 empty. The oils has to be distributed among three people. How will you distribute so that each person gets equal number of bottles and the same quantity of oil?

There is a 5 gallon and a 3 gallon bottle. You also have a hose with unlimited water. How are you gonna make the 5 gallon have 4 gallons using your items? (You don't know the exact dimensions of a gallon)

An old man, Dave, lives alone in a flat. Because of his age , he is not able to move comfortably and hence most of the things used to be delivered to his house. On Friday while delivering the mail, the postman feels something suspicious in the flat and try to look inside through the key hole and he saw the bloody body of the old man. Homicide arrived the scene. On the outside of flat, they find two bottles of warm milk, Tuesday newspaper, some unopened mails and some gifts. Homicide waste no time and find the murderer almost immediately. How did they do it, and who was the murderer?

A wealthy man lives alone in a small cottage. Being partially handicapped, he had everything delivered to his cottage. The mailman was delivering a letter one Thursday when he noticed that the front door was ajar. Through the opening, he could see the man's body lying in a pool of dried blood. When a police officer arrived he surveyed the scene. On the porch were two bottles of warm milk, Monday's newspaper, a catalog, flyers, and unopened mail. The police officer suspects it was foul play. Who does he suspect and why?