Ellis, 55, was incarcerated in a South Dakotas prison under an interstate agreement with Wisconsin, and died Sunday in a Sioux Falls, S.D., hospital of apparent natural causes, the unidentified prison official said.
Ellis was arrested in 2009 after Milwaukee police said his DNA matched samples found on six of the homicide victims and on a can of pepper spray found at the scene of death of the seventh. All seven victims in the homicides, from 1986 to 2007, were strangled, the Milwaukee Journal Sentinel reported.
He unexpectedly pleaded no contest to seven counts of first-degree intentional homicide at his February 2011 and was sentenced to seven consecutive life terms, never explaining in court why he committed the crimes over a 21-year period, the newspaper added.
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