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ST. LOUIS – A man pleaded guilty Wednesday to involuntary manslaughter for the death of his sister.

Fifteen-year-old Alicia Anderson was shot to death in August 2013 at the family's home in the 4600 block of San Francisco in north St. Louis.

Marcus Anderson, 21, was sentenced to two years of probation. Authorities say he has a mental disability and thought it was a toy gun.

The gun belonged to a family friend, who left it there.