Thirteen healthy dogs awaiting adoption at Jefferson Parish's animal shelter died after a kennel worker sprayed them and their water bowls with an improperly diluted insecticide, then closed up and left for the night.

When other workers opened the shelter the next morning, they found two animals dead and 11 others dying, an official said Wednesday.

Emergency treatment saved two other dogs that were harmed by the chemical Pro-Late/Lintox, a substance that parish officials said had never previously been used at the shelter.

"Everyone realizes that this is a major tragedy, and there will be major consequences," said Bert Smith, deputy chief administrative assistant to Parish President Aaron Broussard and formerly director of the animal shelter.

Smith is overseeing an internal investigation that has generated stringent new policies and additional supervisory staff at the shelter. The results of the probe will be turned over to the sheriff's office to determine if any criminal charges will be filed.

The inquiry also could result in disciplinary action against two kennel employees who had some role in the March 23 incident. A third kennel worker — the one who actually sprayed the insecticide — has resigned, Smith said.

The other two were placed on leave pending an investigation of the incident. There names were not released.

Smith said he doesn't yet know why the chemical was sent to the animal shelter. It is generally used on farm animals or plants, and the label directions make no mention of use on domestic animals, he said.

But even if not the product of choice, that is "no excuse" for the outcome, Smith said. "If it had been properly diluted and properly applied, as the kennel vet would have spelled out once he reviewed it, there is no reason to think it would have caused a problem," he said. "But it never got to that point. The vet never saw it."

One of the two surviving dogs was adopted Saturday. The other is scheduled for release to a rescue organization as soon as it heals from a skin condition unrelated to the spraying incident.