Alice Uden is accused of killing her ex-husband back in the mid-1970s in Wyoming.
Investigators say his body was recently found in a mineshaft.
Her husband, Gerald Uden, has been accused of killing his former wife and her two children, who disappeared in 1980.
No remains have ever been found.
The sheriff of Christian County, Missouri said he's stunned the couple has been living nearby with this dark secret for decades.