Subordinate clauses embedded within subordinate clauses

Relative pronouns like who, that and which introduce a relative clause. Since these relative clauses can’t stand by themselves, they are subordinate clauses. Moreover, these relative clause function in three ways: as noun clauses, adjectival clauses or adverbial clauses. You can embed a subordinate clause within a noun clause. However, how will the rules of comma usage function then?

Is it:

The boy knows that if he kills the woman, he will be sent to prison.

Or:

The boy knows that if he kills the woman he will be sent to prison.

Why I’m asking this question is that this isn’t your normal subordinate clause that begins with subordinate conjunction. A subordinate clause that begins with a subordinate conjunction doesn’t come after a verb, but this does; so how will the rules function in this case.

The boy knows [that if he kills the woman he will be sent to prison].

The subordinate clause in brackets is a declarative content clause introduced by the clause subordinator "that", and functioning as complement of the verb "know".

Within that clause is a conditional construction, where the protasis consists of the preposition phrase "if he kills the woman", in which the subordinate clause "he kills that woman" is complement of "if". The apodosis consists of "he will be sent to prison", i.e. the matrix clause minus the protasis.

A comma between the apodosis and the protasis is optional.