TOWSON, MD., SEPT. 14 -- Baltimore County police have revised their theory on the slayings of two pregnant sisters and their husbands near Essex last weekend, saying it might have been a premeditated attack in a drug-stealing scheme.

Police developed the new theory Sunday after seizing 17 one-pound plastic bags of marijuana from a garage in Baltimore, said Jay Miller, a police spokesman.

Miller refused to reveal the location of the dwelling where he said police were led by a tip from an unidentified acquaintance of one of the two men charged with the killings.

Police believe the marijuana was taken from the victims' home and hidden there after the killings.

The theory differs from accounts given by police Friday when they arrested and charged two men -- Rico Marzano of Baltimore and Robert Michael Huesman of Essex, both 19 -- with six counts of homicide.

Police originally believed the slayings resulted from an argument over the price of a pound of marijuana that was being sold from the home where the killings took place.

Police now think that the slayings were part of a plot to steal marijuana.

The victims were Donald Francis Nolan, 35; his wife, Valerie Joan Nolan, 31; Valerie Nolan's sister, Laurie Ann Kroll, 26, and Laurie Kroll's husband, Kavin Kroll, who was in his mid-twenties. All four were found face down on the living-room carpet of the Nolan home, with bullet wounds in the backs of their heads.

Marzano and Huesman were ordered held without bail Saturday at the Baltimore County Detention Center in Towson.

Police believe Nolan and Kroll were selling marijuana out of the Nolan home and were being supplied by at least one Mexican connection out of Texas.