HUNTINGTON BEACH, Calif. — Beth Webb remembers talking with friends at her sister’s Christmas party several years ago, wondering aloud if she would support the death penalty if someone she knew were murdered. Then, in 2011, her sister, Laura Webb Elody, was killed along with seven other people as she worked at a hair salon in nearby Seal Beach.

For weeks, Ms. Webb wanted revenge. And the local district attorney promised she would get it in the form of the death penalty. But five years later, the man who killed her sister and wounded her mother is still alive, and Ms. Webb is now helping to lead the campaign to abolish the death penalty here.

Tami Alexander has waited even longer. The man who killed her mother-in-law and sister-in-law has been on death row for more than two decades.

The death penalty has long been one of the most contentious issues in the state. Though California has executed only 13 people since the 1970s, it has sentenced hundreds to death and has more prisoners on death row than any other state. California has repeatedly been criticized for keeping those people in a suspended state for years, costing Californians billions of dollars.