BOSTON (Reuters) - A Vermont woman who planned to poison herself manufactured the deadly ricin substance in the retirement home where she lived and tested it on her fellow residents, federal officials said in court papers.

Betty Miller was charged on Thursday with violating U.S. laws that prohibit possessing biological weapons after tests revealed that she had manufactured ricin powder at the Wake Robin retirement home in Shelburne, Vermont.

Federal prosecutors on Friday asked a federal judge in Burlington, Vermont, to order her held without bail, citing concerns that she could harm potential witnesses.

Miller, whose age was not disclosed, told staff at the facility that she had begun manufacturing the powder from the seeds of castor oil plants grown onsite, according to a Federal Bureau of Investigation affidavit filed at the court.

The FBI said in court papers that Miller told investigators that she had researched how to make the poison and that she had wanted to harm herself with the powder but first sprinkled it on other residents’ food to test its strength.

No other residents of the facility showed signs of ricin poisoning.

A representative of the retirement home did not respond to a call seeking comment.