A Shelton woman faces multiple counts of threatening after she allegedly sent letters containing a suspicious substance to St. Vincent\u2019s Medical Center. Theresa Burden, 37, of 71 Sachem Drive, Shelton, was charged Feb. 26 with four counts of first-degree threatening. She was held on $50,000 bond. Bridgeport Det. David Garcia led the investigation, assisted by Lt. Chris Lamaine. A nursing student Burden is a student of the St. Vincent\u2019s School of Nursing, and the charges stem from threatening letters containing a suspicious substance that have been sent to the hospital commencing on Dec. 12, 2012. The letters caused alarm on numerous occasions within the institution, resulting in the hospital closing portions of the facility until the substance could be analyzed by state and federal authorities. Motive not established Police said Burden was arrested at her home without incident and the motive for sending the letters has not been established. The investigation is ongoing, according to Bridgeport Police Capt. James Viadero, head of the detective bureau. The State Police are investigating a similar case in which threatening letters containing a similar substance were sent to Gov. Dannel P. Malloy. No arrest has been made in that investigation.