Marilyn Howell, 63, of Bear, Del., and her son, Robert, 32, were arrested in late February after a raid on their home, WCAU-TV, Philadelphia, reported. Investigators found more drugs, an AK-47 and other weapons, police said.
Howell mailed the package in November from a self-service kiosk, Brandywine East Community News in Delaware reported.
The U.S. Postal Service returned the package to the return address, which was not Howell's, WCAU said. When the person at that address found hallucinogenic mushrooms and prescription drugs, he turned it over to police, setting off an investigation that included postal inspectors.
Bail was set at $76,500 for Howell and $10,500 for her son.
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