The first and third sentences sound the most natural in casual spoken English, with the third one being the best choice. Here's why: 1. "I don't remember if it was him who was holding the gun or if it was me." - Natural and correct, but slightly formal for casual speech. 2. "I don't remember if it was him the one who was holding the gun or if it was me." - Grammatically awkward. The phrase "him the one" feels redundant and unnatural. 3. "I don't remember if it was him holding the gun or if it was me." - This is the most natural and conversational. It’s concise and easy to say. Suggested Alternative: If you want to make it even more casual: - "I don’t remember if he was holding the gun or if I was." Focus on keeping sentences concise in casual speech—shorter phrases like "him holding the gun" sound more natural than overly detailed structures.

In speech they are wrong or unnatural. You would say: I don’t remember who was holding the object - him or me.

You can say "It was him" or "It was he". However, if you follow that with "who was holding something" then it is better to say "It was he". The reason is that "he" and "who was holding something" stand in apposition. That means they are parallel noun expressions that stand for the same thing. Since "he was holding", not "him was holding", "he" just sounds much better. My choice would be. "I don't remember whether it was he who was holding the thing, or if it was I." (if you wonder why I said "thing", it is because there are many words that the iTalki filters don't like)

The second sentence is incorrect: you can't say, '. . . him the one . . ." The other two sentences are fine.