Brittany Wilson, 32, was found outside the Cape Girardeau home she shared with 34-year-old Harrison Stephen Foster with blood on her clothing and a sword lying in the front yard.
Wilson had called police shortly after 11p.m. on Friday to report that she had killed Foster with a sword, cops said.
She told investigators that she believed he had several other entities living in his body, and she was setting him free by stabbing him, police said
After officers arrested Wilson, they went inside the home and found her Harris dead with several fresh stab wounds.
Wilson and Foster were planning to get married after they sharing on Facebook their engagement on April 17.
