Police says Riess murdered Pamela Hutchinson then stole her credit cards, vehicle and assumed her identity.
This undated photo provided by the Dodge County, Minn., Sheriff's Office shows Lois Riess, of Blooming Prairie, Minn., who is being sought in connection with the killing of a Florida woman.
Riess is also accused of murdering her husband, David, in Minnesota before heading south to Florida.
"She smiles and looks like anyone's mother or grandmother, but she's calculating, she's targeting and she's an absolute cold-blood killer", Carmine Marceno, a deputy sheriff in Lee County, Florida, told NBC News on Florida, after authorities lost Riess' trail.
Police say Riess is considered armed and extremely unsafe, despite her age and appearance.
Officers did, and found him dead of gunshot wounds at the worm farm on March 23, the sheriff of Dodge County said.
Riess is also wanted on felony theft charges for allegedly transferring close to $10,000 from a bank account for her husband's business to another of his personal accounts before forging his signature on three checks totaling $11,000.
Riess, who is considered armed and unsafe, is believed to be driving Hutchinson's white Acura TL with a Florida license plate of Y37TAA.
Anyone with information on Riess' whereabouts is asked to call the Minnesota Bureau of Criminal Apprehension Tip Line at 1-877-996-6222.
"It's just evil that flowed through".
She had left Iowa by the time police tracked her there in late March, the BCA said.
Marceno said Hutchinson's white 2005 Acura TL had been spotted in Louisiana and around Corpus Christi in the days after Hutchinson's body was found.
"As her resources go away she may become more desperate and God forbid may strike again", said Marceno.