Must be and must have been

Question

Is any of these sentences correct?

There must be something happened in the past that traumatized him.

There must have been something happened in the past that traumatized him.

And;

Do I need to add 'that' after 'something'?

Like, There (must be or must have been) something that happened in the past that traumatized him.

Answer 1

There must have been something that happened in the past that traumatized him.

To me the first sentence has mixed tenses: "be" conflicts with "in the past".