The former Wellesley College student who was found not guilty by reason of insanity of stabbing her former boyfriend as he slept in his MIT dorm room was allowed to go free yesterday, after a judge decided not to have her committed to a psychiatric hospital, her attorney and a prosecutor said.

Anna Tang, 24, of Brighton, was initially charged with armed assault with attempt to murder in 2007 after prosecutors accused her of sneaking into Wolfe Styke’s dorm room and stabbing him while he slept. Tang admitted stabbing Styke, but maintained that she was not criminally responsible by reason of mental illness.

Tang waived her right to a jury trial and on Jan. 8, Judge Bruce Henry found her not guilty by reason of insanity of armed assault with attempt to murder, home invasion, and assault with a dangerous weapon causing serious bodily injury, Tang’s lawyer Robert A. George said yesterday.

After her acquittal, Tang was sent to the Solomon Carter Fuller Mental Health Center in Boston for evaluation. Yesterday, at a commitment hearing in Middlesex Superior Court, Henry decided against having her committed to a mental health facility and ordered her to be released.