It's likely the dog drowned, Liberto said.
David and Linda Wirta were temporarily housing Hunter, his five siblings and Hunter's mom, who had been surrendered at a shelter in April.
"We have had seven wonderful weeks with these puppies and to have this happen to Hunter just a week before he could go to his forever family has been devastating," Linda Wirta wrote in an email Friday.
David Wirta said the drainage pipe was covered, but the puppies somehow got the cover off by either biting or clawing at it and Hunter fell in.
About 4:15 p.m., the family discovered what happened and called their handyman service, JTC Estates, which dug a hole to expose the pipe in the side yard of the home. They sawed off part of the pipe in an attempt to reach in and grab Hunter.
"Because of the echo of a pipe, we thought the puppy was very close," Linda Wirta said. "The reality is, he [was] probably a considerable distance away from where we were digging."
After a couple hours of effort, the Wirtas called the Fire Department for help.
"They were incredible," Linda Wirta said.
After three more hours of searching and finding no trace of the puppy, the Wirtas opted to suspend the search.
"Nobody wanted to end the search, but it was becoming clear what must have happened," Linda Wirta said.
The Fire Department previously reported that the pipe was left uncovered while work was being done on the home's piping system, but the Wirtas disputed that.
"We were not having any work done, and in fact, we previously had a vet and a handyman service puppy proof that part of the yard just to keep the little guys safe," David Wirta wrote in an email Friday.
Despite Thursday's tragedy, Linda Wirta said fostering the puppies has been wonderful and she encourages others to foster animals who need help.
"While it has been a lot of work, the sheer joy of connecting with my three teenage kids over the gift of foster puppies has been priceless," she said.
Linda and her daughter, Kate, spent Thursday night sleeping with the rest of the puppies, which she said brought some measure of comfort after this " freak accident."
"I wish this story had a happy ending," Linda Wirta said.