Christopher G. Nichols, 27, was sentenced Tuesday for gun theft, trafficking in stolen property, being a felon in possession of firearms and other crimes, The Spokesman-Review reported.
Prosecutor Tim Rasmussen said sentences for the gun crimes must be served one after another, as a result of Washington's 1995 law known as Hard Time for Armed Crime.
Nichols and his lawyer took the case to trial after turning down a plea deal that could have reduced his sentence by about 100 years.
Nichols, who had no role in the 2011 killing of Colville resident Gordon Feist, wept as the sentence was read, Rasmussen said.
Rasmussen defended the sentence, saying the burglary was "the root of this violent and senseless killing of Mr. Feist, who was acting as a good Samaritan when he was killed.
"This law has been upheld many times in appellate court," Rasmussen said. "It represents a decision by the Legislature to strike at the root of violent crime."
The crime that netted Nichols what amounts to a life sentence began on June 28, 2011, when he and Eric L. Booth, 26, broke into a home in Stevens County and stole a safe containing several firearms.
Booth then planned a ruse with 27-year-old Jesse J. Fellman-Shimmin and 25-year-old Collette M. Pierce to burglarize the home of Feist, 63, who served three tours in Vietnam as a Navy SEAL.
They pretended they had run out of gas, and Feist agreed to help. Feist was driving the suspects back to their car with gas when Booth shot him in the head using one of the stolen guns.
All three later reached plea agreements for their roles in the killing and testified against Nichols.
Stevens County Superior Court Judge Pat Monasmith previously sentenced Fellman-Shimmin to 25 years in prison for second-degree murder; Booth was given 26½ years for first-degree murder; and the judge gave Pierce 15 years for second-degree murder.
Rasmussen said he believed Nichols' sentence of 125 years was one of the longest sentences ever handed down for a non-murder conviction.
"Without the burglary of these firearms, this killing would not have occurred," he said.