Mary Ann Becker was 16 years old when her mom found her dead in her Atkinson, Illinois home.
"The cause of death was strangulation," said Terry Patton, Henry County State's Attorney.
It was September 9, 1974.
"Police investigated it at the time and were not able to come up with sufficient evidence to charge anybody," said Patton.
"I've got one agent that's focusing almost full time on this case," said Illinois State Police Master Sgt. Chris Endress.
At the beginning of September, Henry County Crime Stoppers announced a $15,000 reward for information leading to an arrest and conviction in the case.
"When Henry County Crime Stoppers put out that reward money that did generate a lot of phone calls," said Endress.
At the end of September, Mary Ann's body was exhumed and was sent to Bloomington for an autopsy. Her body was reburied in a private ceremony the next day.
"We wouldn't have gone to this step if we didn't think it was vital to the case," said Endress.
"You can't leave any stone unturned and if there's a possibility with coming up with evidence that helps solve the case, we need to do it. And forensic evidence, the science has advanced so much in the last forty years it was definitely worth doing," said Patton.
"We're hoping that there could be suspect DNA underneath her fingernails. We're of course looking at sex assault evidence if there's still any remaining," said Endress.
To help bring closure to those who knew Mary Ann Becker.
"We're very hopeful that it will produce some benefits and bring this case to an end," said Endress.
"And we want to solve this case for the family so they can get some answers and have some closure in the case," added Patton.
The evidence from the autopsy was sent to the Joliet crime lab. It could be months before the results are returned.