Updated 10/07/13 – 4:45 p.m.

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CHICAGO (CBS) — A 61-year-old Oak Lawn woman has been charged with the sledgehammer and knifing death of her baby granddaughter.

Oak Lawn Police said Alfreda Giedrojc, of the 6600 block of West 91st Street, has been charged with one count of first-degree murder in the death of her 6-month-old granddaughter. The South Suburban Major Crimes Task Force identified the girl as Vivian Summers.

“I have never seen anything like this. It’s a tragedy,” Oak Lawn Police Chief Michael Murray said at a Monday news conference. “Our thoughts and prayers go out to the family. This is going to be a very difficult time for everybody.”

Prosecutor Michael Deno described an unusually horrific crime. Giedrojc allegedly laid the girl on the floor when she was alone with her and then retrieved a sledgehammer from a closet she had placed there the night before.

After striking the baby multiple times, the baby was still crying and moving, so the grandmother slit the child’s throat with a large carving knife, Deno said.

Giedrojc was being held without bond at the Cermak Hospital in Cook County Jail, for continuing observation.

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Oak Lawn police officers initially were called to Giedrojc’s home around 10:45 a.m. Sunday after receiving a call about a person with a gun. While en route, police learned a baby had “suffered a significant injury,” Oak Lawn police said.

Prosecutors say Vivian’s father and Giedrojc’s spouse, the girl’s grandfather, went across the street to visit another relative before the crime occurred.

After police arrived at the home, Vivian was taken to Advocate Christ Medical Center in Oak Lawn and was pronounced dead shortly before 2 p.m. Sunday.

Police said Vivian lived in Bolingbrook with her parents.

A neighbor said Vivian’s grandparents have lived at the house in Oak Lawn for years, and their children and grandchildren visited often.

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“We’ve seen babies, we’ve seen kids, … because they’ve even got a grandson who’s one of our grandkids’ age,” Caren Hennessy said. “So, a couple of grandkids. It’s sad; sad. Our heart goes out to everybody.”