The force handed a file to the Crown Prosecution Service relating to two of the men after it was decided no further action would be taken against a third.
The CPS said today: "This has been examined in detail and we have informed Leicestershire Police that there is insufficient evidence for a realistic prospect of conviction, in that the conduct shown is not sufficient to prove a criminal offence under the Animal Welfare Act 2006."
We can confirm there has been an incident involving one of our animals. Twycross Zoo's team are working to resolve the situation as quickly as possible, whilst ensuring the safety of the public and staff. The zoo is closed at present however we anticipate the zoo will reopen today and we will update you at 12 noon.
Twycross Zoo have announced that the gorilla born in early January is a boy.
Mum, Ozala, gave birth on 3rd January 2013. Ozala, was, at first, very protective of her newborn and so staff were unable to get close to the infant.
“Ozala was so protective of her newborn infant that she held it very close and it is only now that the infant is bigger, and Ozala has become more relaxed, that we have been able to see the infant closely enough to determine its gender."
Charlotte Macdonald, Curator of Living Collections
The western lowland gorilla is a critically endangered species.