past vs past perfect - "He had a gun." or "He has had a gun."

What is the difference between the sentences

1. He had a gun.

and

2. He has had a gun.

I think when you are saying about the past why don't you just say it as "He had a gun" instead of "He has had a gun"?, this goes same with these below sentences as well.

1. He has killed.


2. He has had killed.

1. She had sex before she died.


2. She had had sex before she died.