A serial killer died on Sunday after serving less than three years of a life sentence for strangling seven women, according to South Dakota prison officials.
Walter Ellis, 53, died at a Sioux Falls hospital, apparently of natural causes, but an autopsy is being conducted as part of a standard investigation by the South Dakota Department of Corrections, the officials said in a statement.
As police searched for a suspect in the killings of seven Milwaukee women from 1986 to 2007, local media dubbed the killer "the Milwaukee North Side Strangler."
Ellis, arrested in 2009, was sentenced in February 2011 to seven consecutive life sentences with no possibility of parole. He pleaded no contest to first-degree intentional homicide in the strangling deaths of the seven women, who ranged in age from 16 to 41.
Police said Ellis' DNA matched semen samples found on six victims and a blood sample on a can of pepper spray discovered at the seventh murder site.
Ellis, who was from Milwaukee, was housed in a South Dakota prison under an interstate agreement.