How does one determine the difference?

This morning, as I was working I received a CNN News update.
Heath Ledger's death was an "accidental" overdose.

How does one determine the difference between an accidental or
intentional overdose? Is it the amount of drugs in the system? Is it
the combinations used? And if it's the combination that is doctor
prescribed - where is the culpability and responsibility of the doctor?
Isn't it their responsibility to ensure that their patients aren't
taking medicines that if accidentally combined, will cause an
"accidental" overdose?

Often, you will hear of accidental overdoses when a person mixes alcohol
and drugs. Who's to say that was truly accidental? I know that Heath
Ledger had everything to live for...and no one saw this coming. But I'm
not entirely convinced that the ruling of accidental overdose is
entirely accurate.

How can one speak to an individual's state of mind - isn't it possible
that maybe someone intentionally mixed or took a combination of the two.
Here's my thing. The following drugs were found in his system in this
"accidental overdose": Oxycodone is a painkiller (Percocet), Hydrocodone
is also known as Vicodin, Diazepam is commonly called Valium, Temazepam
treats anxiety or sleeplessness, Alprazolam is known as Xanax, and
Doxylamine is a sedating antihistamine often used as a sleep aid.

I'm sorry kids. That's an intentional overdose in this girl's mind.