It wouldn't show up in a routine tox screen unless it was in the system at that time. Hair tests will show up earlier drug use.
Incorrect. Tests will come up "positive" for THC up to 30 days after use.
But at what levels? I don't know much about THC levels, but given that some people rushed to point out that there can often be a "spike" in the levels right after death, the amounts the autopsy found must have been kind of high.