The plane made a scheduled stop in Detroit, where Delta says a flight attendant checked on Alejandro at 6 a.m Wednesday.
When the dog was checked on again between 8:00 a.m. and 8:30 a.m., Alejandro was dead, according to Dellegrazie's attorney, Evan Oshan. "Delta is conducting a thorough review of the situation and have been working directly with Alejandro's family to support them however we can", the airline said in a statement.
Oshan also represented the owners of Koketo, the French bulldog who was killed on a United Airlines flight back in March.
And last Tuesday, a woman traveling from OR to Kansas with her family on a United Airlines flight was stunned when she went to collect her dog from the cargo facility and instead discovered a Great Dane waiting in its place.
A dog died during a short layover in Detroit during a Delta flight.
Alejandro was found dead on a layover in Detroit in the space of a half-hour.
Delta spokeswoman Lisa Hellerstedt told CNN there was "vomit and fluids" in the dog's cage.
"When he landed here in MI, he was alive at 6.30am and then at 8.20am, he wasn't moving and it just doesn't make any sense to me", owner Michael Dellagrazie told WDIV-TV. "This is essentially their family member who died".
Delta is not among the airlines that recently changed their policies about transporting pets in cargo in Phoenix and other desert cities.
They plan to take the dog's remains to an independent agency for an autopsy to determine what caused the death. "As part of that review, we want to find out more about why this may have occurred to ensure it doesn't happen again".
This is just the latest controversy for the commercial airliners involving dogs.
A day after that incident, a 10-year-old German shepherd named Irgo was flown to Japan when he was supposed to end up in Kansas. The flight was going from Newark to St. Louis, but the pet was due to fly from New Jersey to Akron.
According to the Department of Transportation, 506,994 different animals were flown on USA airlines in 2017.