Deputy U.S. Marshal John Kinsey said 56-year-old Lois Ann Riess was nabbed as she sat in a restaurant and was taken into custody without incident.
Authorities caught Riess after receiving a tip from an eyewitness that someone matching the fugitive's description was at the restaurant, a spokesperson for the South Padre Island police said in a statement.
The deputies approached her at approximately 8:25 p.m. local time, confirmed her identity, and arrested her, the statement said.
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Riess is accused of two murders: that of her husband David in their home state of Minnesota in March, followed by the Florida murder of Pamela Hutchinson, whose body was found in a condo April 9.
Officials alleged Riess gunned down the 59-year-old new acquaintance because the two looked similar and the victim's identity could thus be more easily stolen.
"I promised all along that Lois Riess would end up in a pair of handcuffs," Lee County, Florida, Undersheriff Carmine Marceno wrote in a Facebook post Thursday night. "Tonight, she sits in a jail cell in Texas. We are working as expeditiously as possible to bring her back to Lee County to face murder charges."
Hours before Riess was spotted, the Dodge County Sheriff's Office in Minnesota released surveillance video obtained by investigators that showed Riess buying a sandwich at a gas station convenience store in Northwood, Iowa, last month, and asking for directions south out of the state.
"This is the only video investigators have located to date with audio of Riess speaking. Investigators hope that her voice on this video, in addition to other videos and images released, will help someone recognize her and report her whereabouts so she can be taken into custody before anyone else gets hurt or killed," officials wrote, adding that Riess was last seen driving Hutchinson's white Acura TL.
After Riess was captured, deputies also seized a 2005 Acura from the scene for forensic processing.
Authorities this week said the suspect had been traced to Louisiana and Texas after Hutchinson's murder. Detectives in South Padre Island were working with Minnesota and Florida authorities concerning the outstanding felony charges.
After the second murder, Riess allegedly withdrew $5,000 from Hutchinson's account, went to a Hilton hotel in Ocala, Florida, and used her identity.
"You would never suspect she's using an ID from a victim," Marceno said.
The list of allegations against the grandmother included murder, grand theft auto and identity theft.
If Florida prosecutors find that the murder of her lookalike was premeditated, Riess could face the death penalty.