A nurse convicted of killing four of her patients was given life in prison this week in the Netherlands, a country that rarely imposes its harshest sentence. Lucy de Berk, 41, had been on duty during 13 mysterious deaths, including that of a 6-month-old. A statistician said the chances of her being only coincidentally on duty during each death was 1 in 342 million. She went about her work in a refined and calculating way, said Judge Jean Kalk. Apparently she believed she was qualified to hold the power of life and death over these people. An expert from the U.S. FBI testified that de Berk fit the classic profile of a serial killer.