An Indiana man charged in the killings of seven women who prosecutors said were among a vulnerable population of drug addicts or prostitutes pleaded guilty to murder charges on Friday to avoid facing the death penalty, officials said.

The man, Darren D. Vann, 47, preyed on those who were disconnected from their families and could not be readily found, Bradley C. Carter, a spokesman for the Lake County prosecutor’s office, said.

The victims fell into lives of drugs or prostitution and “the families knew they were spiraling downward and there was nothing to do,” Mr. Carter said. “They all knew this lifestyle would not end well.”

Mr. Carter said prosecutors agreed to a plea deal in which they would no longer seek the death penalty. He said officials wanted to spare relatives of the victims the prolonged court battles that would have come with a death penalty case.