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.

Question: What happened after Cho was diagnosed with selective mutism?
Self-contained rewrite: What happened after Seung-Hui Cho was diagnosed with selective mutism?