Who gave Daniel Smith the drugs that killed him?

Pathologist Cyril Wecht, hired by the Smith family to investigate the death of Daniel Smith, said the 20-year-old died of an accidental but fatal interaction of three drugs: anti-depressants Lexipro and Zoloft, and methadone, a painkiller used mostly to treat heroin addiction.
In an interview with Reuters, Wecht said Anna Nicole Smith did not know her son was taking methadone and had no knowledge of any heroin use by him. But isn’t that hearsay unless Wecht gave her a lie-detector test?
"This is one of the mysteries remaining in this case -- why he was taking methadone. It could have been as a painkiller. It is a legitimate drug for that use. His family is shocked. ... I am told that Mrs. Smith was completely in the dark about Daniel taking it," he said.
Wecht was hired to find out what killed Daniel Smith while he was visiting his mother on September 10 in her hospital room in Nassau in the Bahamas shortly after she had given birth to a daughter.
Of the three drugs found in Daniel Smith's body, only Lexipro had been prescribed.
Wecht said he had not been told where Daniel Smith had gotten the drugs found in his body.
"There is now no reason to go ahead with the inquest because there is nothing to suggest foul play. But that would be up to a magistrate in the Bahamas to decide," Wecht said.
I think someone needs to explain who gave the non-prescribed drugs to Daniel. A doctor on Entertainment Tonight said that Daniel was suffering from back pain but that although methadone is used as a painkiller, usually, something not as strong (or as addicting) is used, such as vicodin.
If indeed Anna Nicole Smith and Howard K. Stern married this morning it seems very suspicious to me. Husband and wife can be legally protected from testifying in court to incriminate each other. I think there’s still a lot of questions unanswered. All in all, Daniel Smith led a short, tragic life with an untimely end.