Heckert was arrested this week after new DNA collection and testing technology prompted a review into the case in 2014, reports ABC.
News.com.au reports that Heckert, then known as Carolyn Coon, and DeLeon were dating the same man at the time of her murder.
The 48-year-old real estate agent and mother of two is currently being held on $1 million bail and is awaiting extradition to Kansas.
Over the years DeLeon’s death has often been linked to another unsolved murder, after 26-year-old Diana Marie Ault was shot to death in her Missouri home while her 4-year-old son and 6-month-old daughter were home.
According to the Daily Mail, Ault was the wife of the man Heckert was having an affair with.
So much were the cases linked that the families of the two women were in contact and had even held joint memorial services.
Kansas City police have not commented on a link between Heckert and Ault’s death, but they have previously considered a connection between the cases.
In May, Det. Scott Howard said that the suspect in the DeLeon case, who was at that point still unnamed, "and an accomplice have been involved in other incidents involving the harassment and intimidation of romantic rivals."
They also added that they were seeking further information about a 1987 abduction that may also be related.
DeLeon's mother Gail Elieson told ABC she was "quite pleased" with the announcement of charges in the case.
"It just took a long time to get to this point, It will be 27 years in December."
“She had no enemies. Everybody loved her,” Elieson added. “She did not live a high-risk lifestyle.”