Chose the correct relative pronouns in accordance with the sentence

The criminals, two of ___ managed to escape, broke into a bank.

The correct answer is: Whom

The correct answer is "Whom".
Here, we get two distinct sentence segments, namely "The criminals broke into a bank", and "Two of the criminals managed to escape". "Criminals" is the common portion which must be substituted for a relative pronoun to link the two parts. Among the given options, "Whom" is the most suitable alternative to be placed along with a preposition(Of). So, the correct answer is "Whom".