Italian prosecutors have opened a murder investigation following the deaths of a mother and her teenage daughter after a pre-Christmas meal last year. Sara Di Vita, 15, and her mother Antonella Di Ielsi, 50, fell ill after a lunch in their hometown of Pietracatella, a small municipality 260km (161 miles) southeast of Rome. Sara's father Gianni - the former mayor of Pietracatella - was also taken to the hospital, but he later recovered. The couple's eldest daughter was not there that day. Doctors initially attributed their symptoms to food poisoning, but a new focus emerged after laboratory tests revealed the presence of a deadly poison, ricin - even though police do not yet have a suspect. Doctors first thought the infection was due to either fish or mushrooms and discharged the mother and daughter from the hospital. However, their symptoms quickly worsened, leading to their re-admission. Dr. Vincenzo Cuzzone, head of the intensive care unit at Cardarelli hospital, reported that liver failure developed first, followed rapidly by multi-organ failure. Initially, the deaths were attributed to medical negligence, resulting in investigations of the doctors involved. Test results conducted in laboratories in Italy and Switzerland confirmed the presence of ricin, a highly toxic chemical naturally found in castor beans, which can cause rapid organ failure and has no known antidote.