LAS VEGAS -- Criminal animal cruelty charges probably won't be filed against the Lied Animal Shelter because investigators couldn't substantiate allegations made in a blistering external report.

City officials said the Humane Society of the United States cited confidentiality and did not provide investigators with sources and documentation. The president of the national organization said criminal charges weren't the goal. He said Lied officials invited Humane Society investigators in because they wanted to improve.

Officials from the Humane Society visited the shelter in February. The shelter was temporarily closed because of parvovirus outbreaks and eventually 1,000 animals had to be put down.

A May report on that visit found animals had been left sick and dying in their cages, dogs were starving in overcrowded runs, and incoming pets were being housed with diseased animals.