DENTON, Texas -- The Denton animal shelter is changing its procedures after a worker mistakenly euthanized a dog one day before its owners had arranged to retrieve it.

Shawn Snider and Beth Bayless-Snider arrived to pick up their 3-year-old black Labrador mix on May 15 – a day earlier than planned – only to learn a worker had killed it that morning.

The worker apparently didn't notice an entry on the dog's records saying the owners would pick it up May 16, said Lt. Lenn Carter of the Denton Police Department, which oversees the shelter. Lt. Carter declined to name the worker but said she could face discipline once an investigation is done.

"It was definitely a mistake on our part," he said. "It's a really unfortunate incident, and we're going to take steps [so] that it doesn't happen again."

Police Chief Roy Minter visited the owners' Denton home to apologize, but Mr. Snider said apologies aren't enough. He and his wife are asking the city for $206,000 for the loss of the dog and future breeding opportunities, along with "emotional pain and stress."

They also haven't ruled out a lawsuit, he said.

"I'm not going to just let them get away with an apology," he said. "They can't bring my dog back, so the only thing they can do is give me money."

The couple filed a liability claim dated May 22 with the city's risk management department. City spokesman John Cabrales said officials could not comment on a pending claim.

Mr. Snider said he got the dog as a puppy and named it Amicus because of its friendly nature. The dog fathered three litters of puppies, and the couple sold many of them to supplement their income, he said.

On May 8, animal control officers picked up the dog after it escaped from the couple's yard. A neighbor told officers where the dog lived, Lt. Carter said, so officers left a notice on the door telling the owners how to redeem it.

Ms. Bayless-Snider called the shelter the next day and arranged to pick up Amicus on May 16. They didn't get the dog sooner because they were waiting for payday to afford the recovery fees, which would have been $109, Mr. Snider said.

By policy, the shelter holds stray dogs and cats for at least four days to allow owners to redeem them. If they aren't picked up, animals become available for adoption or euthanasia.

When police officials learned the dog was mistakenly killed, they ceased all euthanasia until May 20 as part of their investigation, Lt. Carter said.