A Pennsauken man pleaded guilty in federal court in Camden yesterday to conspiring to distribute more than 100 grams of heroin.

Jaime Castellar, 31, admitted he rented a house where heroin was packaged in bulk amounts for resale to other suppliers, and small bags for street sales in Camden, said Greg Reinert, a spokesman for the U.S. Attorney's Office. Authorities said Castellar laced his heroin with the powerful painkiller fentanyl to boost its power.

Investigators came upon what they called a heroin "mill" on July 21 after a naked man ran from the house yelling to neighbors for help. The man said gunmen had forced their way into the house. Workers in heroin mills typically are forced to work in the nude to prevent theft.

Castellar, who was at the house when the gunmen burst in, was hurt in the attack and treated at a local emergency room, but he left the hospital before he could be questioned or detained.

Inside the home, in the shadow of the Betsy Ross Bridge, police discovered nearly a kilogram of heroin and 300 grams of fentanyl in the basement.

Fentanyl-laced heroin is believed to be responsible for more than 100 deaths last year in the Philadelphia region. Fentanyl, up to 100 times more powerful than heroin, is commonly used to supercharge the drug's effects. The 300 grams would have been enough to spike 40,000 doses of heroin.

Following the seizure of the fentanyl at the Union Avenue house, deaths from the lethal mixture trailed off, according to a Drug Enforcement Administration spokesman.

Castellar said he packaged the drugs with at least six other people between November 2005 and July 2006 in the house's basement.

Held without bail since his arrest Sept. 28 in Philadelphia, Castellar also admitted in U.S. District Court yesterday to keeping scales, grinders and glassine baggies at the house for the packaging operation.

Castellar, who faces up to 40 years in prison, will be sentenced Aug. 17.

Contact staff writer Sam Wood at 856-779-3838 or samwood@phillynews.com