Monday was supposed to have been a day of celebration for a Plymouth family. Their dog, Porter, would have turned 6 years old, and the customary party with presents and a home-cooked meal was in order.

Instead, the Docken family is grieving after somebody shot and killed their beloved purebred springer spaniel last week as he was running in the backyard.

"That was a reckless act that hurt us," said owner Chris Docken. "We saw our dog as family, our 'firstborn son.' "

Plymouth police have searched for the person who stuck a pellet gun through an opening in the Dockens' privacy fence and shot Porter at 3:05 p.m. last Wednesday. But as of Monday, no one had been arrested.

Docken has passed out fliers and gone door to door in his neighborhood off Northwest Boulevard in hopes of learning who might have done it. The posters announce a reward for information needed to catch the culprit. Friends and neighbors have rallied around the family of four with cash donations — some from people wishing to remain anonymous — plus a GoFundMe campaign called Peace for Porter. As the day went on Monday, the reward pool grew to more than $9,000, including a $2,000 check one person dropped off in the afternoon.

Docken wonders if someone had a grudge against the dog. The opening in the fence is so small that somebody had to have known it was there, he said.

"We think somebody didn't like our dog," said Docken, who said that he's not received complaints about Porter from his neighbors.

Docken's wife, Sarah, was at home doing her taxes when she looked out the window after she heard a "yelp like she has never heard before," Chris said. Originally, she thought the dog had been poisoned. But after rushing to the vet the family learned the dog had been shot at close range. The bullet entered his right side, passed by his liver and stopped near his heart. Vets worked for more than an hour to save Porter but were unsuccessful.

Chris Docken planned to walk the neighborhood Monday in hopes of turning up clues. He said he hopes it was a random crime; no neighbors have reported any trouble with their pets.

Docken said they will wait a couple weeks to see if the reward money produces anything. If nobody comes forward, he said the money will be given to the Retrievers, a nonprofit that works locally to reunite lost dogs and their owners.

"We may never find out if this was something done on a whim," he said. "We hope somebody will turn on a friend or the shooter will come forward. Porter was such a great dog and we loved him so much."