The Denver Police Department revealed in a news conference on Friday morning that they have learned the man who killed an Aurora police officer more than four decades ago was a serial killer. Police said DNA evidence and genealogy helped investigators link the cold cases together, 4CBS Denver reported.

Debra Sue Corr, an Aurora police officer, pulled Joe Michael Ervin over in June 1981. He then used her own to gun to kill her in what was the first line-of-duty death for the Aurora Police Department. Soon after that Ervin took his own life while in custody on murder charges.

Police say between 1978 and 1981 Ervin killed four women--Madeleine Furey-Livaudais on Dec. 7, 1978; Delores Barajas on Aug. 10, 1980; Gwendolyn Harris on Dec. 21, 1980; and Antoinette Parks on Jan. 24, 1981.

Initially investigators were working on each cold case separately. But eventually DNA evidence helped them link the four victims to the same killer. Next, they used DNA to find a living family member of the suspect. Next, they exhumed the body of the suspect and used DNA to confirm he had killed the four women.

In a news release, Denver police described that sequence of events as follows:

– Between 2013 and 2018, these four cases were linked together by DNA evidence, and three separate searches for familial links in Colorado occurred during this time.– The Denver Police Crime Laboratory began in-house Investigative Genetic Genealogy (IGG) work in 2019, which led to a positive ancestry link to Texas.– A familial search was conducted in Texas in the summer of 2021, which resulted in the identification of a close biological relative of the yet unidentified suspect.– Investigators identified Joe Ervin as a potential suspect, and an exhumation of his remains was conducted in Texas in late 2021 to obtain DNA samples for direct comparison to the crime scene evidence.– The identity of Joe Ervin as the suspect in these four related murders was confirmed through DNA analysis in January of 2022.