Why in the sentence "One suspect was a male youth, while the other was an adult man." we use 'the' before 'other'. I have to explain its function.
In English the is the most frequently used definite article.
We use the definite article in front of a noun when we believe the listener/reader knows exactly what we are referring to.
So, here in the sentence
One suspect was a male youth, while the other was an adult man.
we use the because it is being referred to a definite other