Delta says they are investigating the Pomeranian's death.
A dog was found dead in its crate on a Delta Air Lines flight last week.
The Pomeranian, named Alejandro, was discovered Wednesday in the cargo facility during a layover at Detroit Metropolitan Airport.
Alejandro was reportedly en route from Phoenix to Newark, N.J.
Delta Air Lines said it is "conducting a thorough review of the situation to ensure this does not happen again and [has] been working directly with Alejandro's family to support them however we can."
The airline statement continued: "As part of that review, Delta offered to have Alejandro evaluated by a veterinarian while in our possession to find out more about why this may have occurred. We are disappointed that we were not allowed to have a necropsy performed immediately following this unfortunate situation. The family now has Alejandro and we continue to offer our support."
Alejandro's was one of at least four dog deaths while in the care of a U.S. airline this year, according to CBS News.
One of the dogs died on a Hawaiian Airlines flight in February. The cause of death for that canine, a bulldog, was unknown. A German shepherd died of natural causes on a Delta flight in March.
Perhaps the most well-known was the March death of a French bulldog on a United flight. The 10-month-old puppy was placed in the overhead bin on the orders of a flight attendant and found dead upon landing.
The airline apologized to the family following the incident.
Heartbroken owner Michael Dellegrazie told Inside Edition affiliate WDIV that Alejandro was alive and well at the time he was dropped off.
"He was in their care and they didn't take care of him," said Dellegrazie, who has hired attorney Evan Oshan, the same lawyer who represented the owners of the Frenchie puppy.
"We lost a family member," Dellagrazie said. "That's exactly what happened, and somebody has to be responsible for it."