The Cincinnati Police Department launched their investigation into the incident last Tuesday to decide whether pressing criminal charges against the boy's parents would be necessary.
The boy fell 15 feet (4.5 meters) into the gorilla exhibit on May 28 after crawling through a barrier. Smartphone video images went viral worldwide, showing the massive primate dragging the child through a knee-deep moat as witnesses screamed.
Hundreds of thousands of people rushed to sign online petitions condemning the child's mother for indirectly causing the death of the rare silverback gorilla -- with a virulence that some denounced as a "witch-hunt."
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The prosecutor encouraged those quick to judge the family to reconsider.
"The zoo lost a beautiful animal, and one that many people in this area have enjoyed watching for a long time. But it's still an animal. It does not equate human life," Deters said.
In a statement the family welcomed the prosecutor's decision, saying it was "what we expected" and extended thanks "to all of those who have been praying for us."
"This is one more step in allowing us to put this tragic episode behind us and return to our normal family life," said the family, who last week urged well-wishers to make donations to the zoo.
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Zoo officials opted to shoot the endangered animal -- a 17-year-old silverback named Harambe -- rather than tranquilize it, a decision that's also garnered criticism.
But zookeepers said they worried that hitting the gorilla with darts could agitate him before the sedative released, further endangering the child.
According to the prosecutor the boy emerged from the enclosure "unscathed" despite rough handling by the gorilla.