A forensic pathologist says the powerful painkiller propoxyphene killed Sally Mercer, the wife of prominent surgeon Dr. Charles Mercer, Jr. But what is it?

Propoxyphene is a narcotic, the generic brand of Darvon or Darvocet. It's rarely dispensed these days because its effectiveness is considered to be low, says Pharmacist Polly Cove. It's dangerous because it's slow to leave the system, and extra doses could easily be lethal.

An overdose could lead to death within one hour, adds Cove. Its effects like drowsiness and shallow breathing are felt within 15 minutes.

Court transcripts released Tuesday don't indicate what actual dosage was found in Sally's tissue following a second autopsy and extensive testing in 2003, just that there were massive levels present still nearly 35 years after her death.

Dr. Mercer was arrested June 5 and charged with murdering her in 1968. He posted a $1,000,000 bond June 9, and is scheduled to return for his preliminary hearing on June 26.