Robert Chambers, the infamous Preppy Killer who was busted last fall for dealing drugs to undercover cops, is going to use a "psychiatric 'poly-substance abuse' defense." His lawyer Valerie Van Leer-Greenberg told a judge, "He did not act knowingly" because he was so influenced by drugs.

How influenced? Van Leer-Greenberg said, "He was using 10 to 12 bags of heroin a day," plus he smoked crack and pot and abused the painkiller Dilaudid. Currently at Rikers, Chambers has been given methadone for a few weeks.

However prosecutors contend that Chambers had it together enough to deal drugs. Van Leer-Greenberg agreed to turn over Chambers' medical examinations. And Chambers' live-in girlfriend who was also swept up in the bust pleaded guilty last year and was released.

Surveillance photograph of Chambers from the cops' undercover operation