Killing several people doesn't automatically get someone the death penalty.
Prosecutors sometimes threaten to seek the death penalty against a murder defendant as a way to land a guilty plea to a lesser charge and avoid an expensive trial and lengthy appeals.
The threat also can win a killer's cooperation in closing unsolved crimes or finding long-lost victims.
In the case of Gary Leon Ridgway, that could account for more than 40 cases if he turned out to be the Green River Killer.
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However, King County Prosecutor Norm Maleng repeated several times Wednesday that if he seeks the death penalty in four Green River killings blamed on Ridgway, he won't use it as a bargaining chip.
It's not fair, he said.
"The defendants who only killed maybe one or two (victims) might be charged with the death penalty, while someone who committed scores of crimes might be given a break," he said. "There's not a lot of justice in that type of scenario."
Nevertheless, it's not unusual for serial killers to avoid the death penalty. For instance:
In exchange for his guilty plea to murder, prosecutors agreed to drop their efforts to execute him. He was sentenced to more than 400 years in prison last year.
In Pierce County, prosecutors are putting him on trial for two local killings and will seek the death penalty if he is convicted.
In return, prosecutors quit seeking the death penalty against him.
Bianchi is serving more than 116 years in prison in Washington state.
His four-year killing spree started in Seattle in 1974 and ended in Florida in 1978. He confessed to at least 35 homicides, though some experts believe he might have killed more than 100 people. The state of Florida executed him on Jan. 24, 1989.