CHICAGO, ILLINOIS: Police: Girl, 14, stabs 11 y-o sister 40 times because she felt unappreciated.....The 14-year-old was arrested and was charged with murder. (VIDEO)

(CNN) -- An 11-year-old Illinois girl was stabbed 40 times by her 14-year-old sister, police say, and the reason why has many in the small Chicago-area community of Mundelein reeling in disbelief.

Police found the 11-year-old girl unconscious and in need of medical attention in an upstairs bedroom of the dwelling Tuesday morning. She later died. Because the sister, who called police, initially told officers an intruder was to blame for the attack, authorities briefly placed three schools on lockdown. The truth, when it emerged, was even more shocking. The 14-year-old, authorities say, repeatedly and fatally stabbed the victim -- her half sister -- with a kitchen knife because the teen thought she was ungrateful. more