Without Death, The Lord is Denied his Harvest
Set 75 years in the future, science has found a way to extend the human lifespan. The years of healthy life one can expect to live increases each year with newer healthcare technology to the point where in the former United States there has not had a registered death by natural cause in 25 years. Lifespan is like computer memory, it seems each new year brings out an upgrade.
A small cult has formed that believes it must kill as many people as it can who are in their twilight years, there borrowed years so to speak. And there is a wave of homicides of healthy centigenarians.