(CNN) -- A San Francisco man accused of possessing bomb-making materials in his apartment also bought lethal toxins online, the FBI said in documents unsealed Friday.
Ryan Kelly Chamberlain II was charged this week with possession of an illegal destructive device.
Bomb technicians found a series of items in his house, leading to a manhunt that ended with his arrest Monday. Items included a powdery, green explosive substance, a model rocket motor, ball bearings and an igniter for home-made bombs, according to a different affidavit unsealed earlier this week. It did not list deadly toxins at the time.
But the latest documents detail lethal poisons bought anonymously in dark, encrypted corners of the Web.
"The investigation has revealed that Chamberlain has utilized an anonymous, Internet-based market place known as Black Market Reloaded to facility the unlawful acquisition and possession of biological agents and lethal toxins in California and Florida," FBI agent Michael Eldridge wrote in the latest documents.
Chamberlain bought abrin from a seller in Sacramento in December, the documents allege. He said he planned to use the poison to "ease the suffering" of cancer patients, according to the documents.
Abrin is a natural poison found in the rosary pea plant. It's similar to ricin, but has never been used in terrorist attacks, according to the Centers for Disease Control and Prevention.
In addition, he allegedly bought ground rosary peas and pure nicotine in December and June of last year, respectively.
Nicotine can be used to poison food and water, according to the CDC.
Chamberlain, 42, was arrested near the Golden Gate Bridge after a three-day manhunt. It's unclear if he's entered a plea.
Authorities had been looking for him after searching his neighborhood on a tip that he had "items of great concern" at his home, FBI Special Agent in Charge David Johnson said. He declined to say what Chamberlain planned to do, if anything, or what motivated him.
If convicted of the illegal destructive device possession charge, he faces up to 10 years in prison and a $10,000 fine.