This is the noun phrase:

... the most complicated and sensational of its kind


The possessive pronoun **its** refers back to "the case".

Depending on how you analyze it, in **the most complicated and [most] sensational**, the superlative adjectives are substantives, acting like nouns, or there is ellipsis of an understood plural "cases".


> The  electric car known as The Zoomer is one of the most complicated and sensational of its kind.

If you analyze it as a case of ellipsis:

> The  electric car known as The Zoomer is one of the most complicated and sensational <sup>cars</sup> of its kind.

If you analyze the adjectives as substantives by virtue of their being part of "its kind":

> The  electric car known as The Zoomer is one of the most complicated and sensational of its kind.

**its kind** would refer to the kind of the car known as the Zoomer, namely, "electric cars".


> The  electric car known as The Zoomer is one of the most complicated and sensational of electric cars.