MILWAUKEE (WITI) -- South Dakota Department of Corrections has announced inmate Walter Ellis died at a Sioux Falls hospital on Sunday, December 1st -- of apparent natural causes.
53-year-old Ellis was was serving multiple life sentences for first-degree murder out of Wisconsin.
Ellis raped and strangled seven women in Milwaukee between 1986 and 2007.
On September 7, 2009 Ellis was arrested on suspicion of being the notorious serial killer.
Ellis had been arrested 12 times between 1981 and 1998, when he was sentenced to five years for reckless endangerment.
Ellis was initially charged with two counts of first degree intentional homicide and held on $1 million bail.
The Milwaukee County District Attorney's Office later filed five new murder charges against him: three of intentional homicide and two under the previous statute of first degree murder.
Ellis pleaded not guilty, and stood prepared to defend himself.
On February 18, 2011, Ellis pleaded no contest to the seven murder charges and was therefore convicted despite not admitting his guilt.
On February 24, 2011, Ellis was given seven life sentences, to be served consecutively, without the possibility of parole.
After he was convicted, he was initially held at the Dodge Correctional Institution in Waupun for Assessment and Evaluation in accordance with the Wisconsin Administrative Code, from where he was transferred to the Wisconsin Secure Program Facility in Boscobel, Wisconsin.
In November 2011, Walter Ellis was transferred to the maximum custody unit at the South Dakota State Penitentiary.
He was being housed in South Dakota under an interstate compact agreement. There are currently 27 South Dakota inmates being housed in other states and 28 inmates from other states being housed in South Dakota as part of the compact.
The Division of Criminal Investigation is investigating, as is standard procedure in the death of an inmate.
An autopsy will be conducted.