LONDON -- A British woman who killed three men and attacked two others during a 10-day spree was told Friday that she will spend the rest of her life in jail.

Joanna Dennehy smirked as she was sentenced by Judge Robin Spencer to life with no possibility of parole -- only the third British woman to receive the country's toughest sentence.

Dennehy had pleaded guilty to murdering three acquaintances, whose bodies were found in rural ditches near her hometown of Peterborough in eastern England. After stabbing them to death in March, she drove to Hereford in western England where she stabbed and injured two strangers out walking their dogs.

She also admitted two counts of attempted murder and three of preventing the lawful and decent burial of a corpse.

Passing sentence at London's Central Criminal Court, the judge told 31-year-old Dennehy she was "a cruel, calculating, selfish and manipulative serial killer." He said the killer had written him a letter saying she was not sorry for the murders.

He added that Dennehy told a psychiatrist: "I killed to see how I would feel, to see if I was as cold as I thought I was, then it got more-ish."

One witness told the trial that Dennehy had boasted of killing eight people, though she is not accused of more murders.

Three men were sentenced for helping Dennehy dispose of the bodies and giving her shelter.