Is the の in this question seeking an explanation or changing the verb into a noun-like?

Question

So in the question sentences:

1. 誰が盗んだのか
2. キミが選んだことだろう?

In (1.), I thought that the の there is seeking an explanation.

But I found another sentence (2.) and I know that こと can follow a verb and 物 can follow an adjective to talk about them like nouns. Both can be replaced by の.

So if the の in sentence (1.) is not seeking an explanation and makes 盗んだ into a noun then what has the sentence become and how?

If the の is seeking an explanation then what has sentence (2.) become with 選んだこと(event of choosing)?

More specifically, I am confused with the structure of the following :
(subject + が + verb/adjective + の/物/こと+ か/question).
Please explain as detailed as possible.

Answer 1

こと can follow a verb and 物 can follow an adjective to talk about them like nouns.

This I think is not quite right. もの follows a verb (eg, 食べたもの = "the thing I ate") all the time, and こと follows an adjective (eg, 悪いこと = "an evil thing") all the time. Basically もの is for tangible objects and こと is for intangible things/ideas.

• 君が盗んだのだろう?: の in this sentence is so-called explanatory-no. I think の in this position (between a verb and だ/だろう/です/でしょう) is almost always explanatory の. "You stole it, didn't you?".
• 君が盗んだんだろう?: And such の can often be replaced by ん in speech. "You stole it, didn't you?"
• 君が盗んだものだろう?: This もの refers to the tangible thing which was stolen (e.g., a watch). "This is something you stole, isn't it?"
• [×]君が盗んだことだろう?: This doesn't make much sense because こと refers to an intangible "matter", "event", "situation", etc. You cannot steal a situation.
• 君が選んだのだろう?: This の is explanatory-no. "You decided it, didn't you?"
• 君が選んだんだろう?: The same as above. "You decided it, didn't you?"
• 君が選んだものだろう?: This makes sense if you are talking about some tangible object (e.g., a watch) the listener selected among other options. "It's something you decided on, isn't it?"
• 君が選んだことだろう?: This makes sense if you are talking about someone's intangible decision (e.g., studying abroad, quitting a company). "It's something you decided on, isn't it?"