Conversation so far:
What is selective mutism?
Selective mutism is an anxiety disorder in which a person who is normally capable of speech cannot speak in specific situations or to specific people.
When was Seung-Hui Cho diagnosed with selective mutism?
On August 20, 2007, that Cho had been diagnosed with selective mutism.
What happened after Seung-Hui Cho was diagnosed with selective mutism?
Cho's parents sought treatment for him through medication and therapy.
Was the treatment Seung-Hui Cho's family sought for his selective mutism effective?
Cho continued receiving mental health therapy as well until his junior year, when Cho rejected further therapy.

Question: Why was Cho diagnosed with selective mutism?
Self-contained rewrite: Why was Seung-Hui Cho diagnosed with selective mutism?