CEDAR RAPIDS — Her sister-in-law told her that grief doesn’t end. It is “endured and accepted” as part of life, which Janelle Stonebraker slowly came to learn after her only sibling, 18-year-old Michelle Martinko, was fatally stabbed Dec. 19, 1979. Janelle, 70, of Bonita Springs, Fla., said Christmas seasons were annual reminders of her sister’s slaying — and the fact that nobody had been arrested in all that time.In 2018, she was pleased that Jerry Burns, 66, of Manchester, was arrested on a murder charge for the death.