By Susannah Cullinane, CNN

(CNN) -- A nationwide manhunt is underway for a grandmother known as "Losing Streak Lois" to authorities, who believe she killed her husband last month in Minnesota, then killed a woman in Florida, likely in a bid to steal her identity.

Lois Riess, 56, of Blooming Prairie, Minnesota, was last seen Sunday, about 50 miles from Corpus Christi, Texas, heading south on Highway 77, Deputy US Marshal John Kinsey told CNN.

She is known to have a gambling addiction and often frequents casinos, which accounts for her nickname among local police, according to the US Marshals Service.

Riess allegedly killed her husband in March, then fled to Lee County, Florida, where she is believed to have fatally shot Pamela Hutchinson, 59, sometime between April 5 and April 9 in a condo on Fort Myers Beach, according to Kinsey and a marshals service news release. The body of her husband, David Riess, was found March 23, Kinsey said.

Riess "smiles and looks like anyone's mother or grandmother, and yet she's calculated, she's targeted and she's an absolute cold-blooded killer," Lee County Undersheriff Carmine Marceno told NBC's "Today" on Monday. "Suspect Riess, at some point in time, will have no resources, and she will become more desperate and may kill again."

'Considered armed and dangerous'

"Ms. Hutchinson was targeted by the suspect due to the similarities in their appearance," Marceno said Friday during a news conference.

In describing an April 9 search of Hutchinson's condo, he said, "Ms. Hutchinson's purse was found to be in disarray and all cash, credit cards and identification appeared to have been removed."

"Riess' mode of operation is to befriend women who resemble her and steal their identity," Marceno said, calling Riess a "dangerous fugitive."

Added the marshals service: Riess "bears a striking resemblance to (Hutchinson) and has stolen the victim's driver license, credit cards and 2005 white Acura TL (FL tag Y37TAA)."

Riess is wanted for murder, grand theft of a motor vehicle, grand theft and criminal use of personal identification, Marceno said. She is white, with blonde hair, stands 5-foot-5 and weighs 160 pounds, the Lee County Sheriff's Office posted to Facebook.

"Riess is considered armed and dangerous and should not be approached," Marceno said Friday.

'A triple tragedy'

Surveillance video shows Riess talking with Hutchinson on the evening of April 5 at a brewery restaurant in Fort Myers Beach, according to the Lee County Sheriff's Office, which released the images.

Hutchinson "was a friend to everybody," her cousin, Daniele Watts Jeffreys, told HLN's Ashleigh Banfield. "She's never met a stranger. She's just an open, welcoming woman."

Hutchinson had rented a condo in the seaside town as part of trip centered on spreading a relative's ashes in the area, Jeffreys said.

"It's actually a triple tragedy," Jeffreys said, referring to the purpose of her cousin's trip and her death. "Pam should have left the day before, and that would have actually had her alive. She stayed an additional day."