New York: A mentally-challenged mother in the US has been sentenced to 20 years in prison for killing her five-year-old son by administering him with a salt overdose so that she could write about his illness on social network websites.

Lacey Spears, 27, chronicled her son's illness on a personal blog called Garnett's Journey. "Her actions that day, they were inhuman. They despicable. They were evil," said Doreen Lloyd, Westchester County's assistant district attorney.