A man arrested in January after police found the lethal toxin ricin at his home pleaded guilty Tuesday in federal court.

Steven Michael Ekberg (search), 22, faces up to 10 years in prison for unlawful possession of the substance. He was arrested after someone phoned in a tip to police. Agents who searched his home found a cardboard box of chemicals, including three vials that tested positive for ricin. They also found a submachine gun and two semiautomatic rifles.

Authorities have previously declined to comment on how Ekberg got the ricin (search), a toxin derived from castor beans.

As little as 500 micrograms of ricin, about the size of the head of a pin, can be fatal, according to the federal Centers for Disease Control and Prevention (search).

Defense attorney David Mengers said Ekberg "neither did nor ever intended to harm anyone. I think all parties will concede he is not either a terrorist or a potential terrorist."

A sentencing hearing has not been scheduled.