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(CNN) — A Texas woman pleaded guilty Tuesday to a biological weapons charge after she was accused of sending ricin-laced letters to President Barack Obama and New York City Mayor Michael Bloomberg, prosecutors announced.

Shannon Guess Richardson, 35, pleaded guilty to possession of a toxin for use as a weapon, prosecutors said in a statement.

She could be sentenced to up to life in prison. A sentencing date has not yet been scheduled.

Richardson, an actress, was accused of sending the letters earlier this year.

In June, a grand jury indicted her on charges of threatening the president, mailing a threatening letter to New York City Mayor Michael Bloomberg, and mailing a threatening letter to Mark Glaze, director of Mayors Against Illegal Guns, a group Bloomberg founded and co-chairs.

By Josh Levs