Good evening all of my senior in English, I wanna ask you some questions about grammar that really make me confused, in particular when I am composing a sentence.

A. Which one is correct :
1. There are some people asking me question.
2. There are some people ask me question.

B. Which one is correct :
1. I sam him kill that man.
2. I saw him killing that man.
3. I saw him killed that man.

Could please tell we, which one is correct grammatically? Please provide plausible explanation. Thx Agan