Updated

Five months after authorities launched an investigation into the mysterious deaths of elderly twin sisters at their South Lake Tahoe home, investigators have concluded the 73-year-olds died of natural causes.

El Dorado County sheriff's deputies said Thursday that a window was open at the home, and Joan Miller apparently died from hypothermia after Patricia Miller died of coronary artery disease.

Joan Miller was heavily dependent on her sister for her care.

The twins' decomposed bodies were found during a welfare check Feb. 26, and it appeared they had been dead for several weeks. But deputies were stumped because there was no blood or signs of struggle at the home where the women had lived together for nearly 40 years.

Lt. Tim Becker says authorities are glad to bring the lengthy investigation to an end.