In October, the Jackson Police Department in Mississippi announced the retirement of Ringo, a yellow Labrador retriever with a nose that could detect the faintest smell of drugs. After nine years with the narcotics unit, the department said, he would be going home with his partner, a detective in the department.

But Ringo ended up somewhere else, the police department announced last week.

His handler, Officer Carl Ellis, quietly took Ringo to an animal shelter in a suburb of Jackson, where he waited for weeks for someone to adopt him. A police officer in the suburb texted a photo of Ringo to Randy Hare, a dog trainer in Jackson, Mr. Hare said in an interview on Monday.

He recognized him immediately. Mr. Hare had trained Ringo and another dog, a German shepherd named Alpha, for the Jackson Police Department about a decade ago. Mr. Hare said that while Ringo waited for adoption, the shelter’s administrator started to suspect that Ringo might have been a former police dog and sought the help of an officer who ended up messaging him.

“Why would he turn his back on the dog and surrender his dog like that?” Mr. Hare said, referring to Officer Ellis, in an interview on Monday. “I never dreamed in a thousand years that he would pull this. I thought he would at least call me first and let me help him.”