The notorious Milwaukee strangler dubbed the 'North Side Strangler' died Sunday, falling short from serving seven consecutive life sentences for killing seven African-American prostitutes, Daily Mail reported Monday.

Walter Ellis, the 53-year-old infamous Milwaukee strangler reportedly died of natural causes after serving just three years of his seven consecutive life sentences. The South Dakota maximum-security prison confirmed Ellis death at a Sioux Falls hospital Sunday.

It can be noted that this 'North Side Stranger' made headlines when he got arrested in 2009 after finally being convicted of seven murders through the aid of advances in DNA technology.

Daily Mail wrote that Ellis was able to remain free for a very long time because he had asked a fellow inmate to provide his DNA instead of his own. Thus, authorities weren't able to track him down because his DNA wasn't in the state database. Ellis was imprisoned back then for beating his girlfriend with a hammer in 2001, but he was not charged with the said murders because his DNA didn't match the one authorities found in the crime scene of the seven killings.

Fortunately, after much effort, the investigators found a way to get an accurate sample of Ellis' DNA using his toothbrush. They obtained the right one, which right away matched the DNA in the semen found on the six victims and the DNA found on the pepper spray can of the seventh victim.

All of Ellis victims were strangled to death, while one of them was stabbed aside from getting strangled.

The Milwaukee strangler's victims include: 31-year-old Deborah Harris (killed on October 10, 1986), 19-year-old Tanya Miller (killed October 11, 1986), 25-year-old Irene Smith (killed in November 1992), 28-year-old Florence McCormick (Killed in April 1995), 37-year-old Sheila Farrior (killed in June 1995), 41-year-old Joyce Mims (killed in June 1997), and 28-year-old  Ouithreaun Stokes (killed in April 2007). All of Ellis' victims were identified as African-American prostitutes.

Ellis first pleaded not guilty to the charges, but he later on changed it to no contest; thus, he was convicted of the seven murders. Additionally, police tied the 'North Side Strangler' to other killings sic as the murder of 32-year-old Carron Kilpatrick (another prostitute) and 16-year-old Jessica Payne (a white runaway) in 1996.

Although it was already confirmed that the Milwaukee killer's death was due to natural causes, as part of standard procedure, the South Dakota Division of Criminal Investigation is going to continue investigating on Ellis' death.