I realize my mistake in not specifying that what I said does not pertain to all sleep disorders, or all mental health issues - I apologize for the misunderstanding. As Jab pointed out, snoring is an example of one of many sleep disorders that, in all likelihood doesn't really apply here. To put what I meant another way, sleep is very closely related to our mental health - sleep deprivation can cause impairment in our ability to function, to potentially extreme levels if not dealt with.
One example that is less relevant in the case of the Naval Yard shooter, but still shows a strong link between sleep disturbances and mental issues is with ADHD. There is a decent amount of research linking the two - while it might seem obvious, the point of the matter is that a lack of sleep can create A.D.D. (no H) like symptoms, and that a psychiatric issue such as A.D.H.D. might be the underlying cause for the difficulty sleeping.
http://www.medscape.org/viewarticle/708287_6 - one article of many about this particular connection between sleep disturbances and psychiatric issues.
An article about more general issues of comorbidity of certain sleep disorders and psychiatric issues -
http://www.ncbi.nlm.nih.gov/pubmed/19420207
"Current data demonstrate a high rate of comorbidity between sleep disorders and various psychiatric illnesses, especially mood and anxiety disorders."
As far as my personal expertise, I have no formal training. However several members of my family are medical doctors and there are several members in my family with sleep disorders, so the topic (as well as a deluge of research articles from my father) comes up regularly. Having had sleep issues in the past myself, I have also had the chance to ask other doctors and sleep specialists about said articles and had information verified.
As an aside, when I say "issues", I mean anything from benign symptoms that honestly are hard to consider a "disorder", up to actual medical disorders.
Once again, I apologize for the misunderstanding - I am known for being sometimes rather eloquent, and other times coming up with a terribly useless mishmash of words.