The mountain lion that was killed by a car on a highway in Milford in June likely originated in the Black Hills region of South Dakota, the Department of Energy and Environmental Protection said Tuesday. That 1,500 mile trek may be the longest documented movement by a land mammal.

When the animal was first recovered, the DEEP believed the most likely explanation for its presence in a state that hasn’t had a confirmed sighting of a wild mountain lion in more than 100 years was that the animal had either escaped captivity or was released in Connecticut. Others speculated that it was part of a breeding population here in the Nutmeg State.

But the truth was far stranger.

The DEEP sent tissue samples to labs across the country and found that the cat’s DNA closely matched the genetic structure of a breeding population of mountain lions in the Black Hills region of South Dakota.

At a Tuesday press conference at the department’s headquarters in Hartford, biologist Paul Rego called the news a surprise. Porcupine quills found in the animal’s body had led them to believe the 140-pound cougar had been outside for some time before it was killed by a 2006 Hyundai Tucson. But he said the captivity theory still seemed like the most plausible explanation.

Rego said they were shocked when further tests revealed a direct DNA match to a mountain lion tracked in both Minnesota and Wisconsin from late 2009 to early 2010. Wisconsin biologists even named the animal, dubbing it the “St. Croix Mountain Lion” for the county in which it was first sighted.

It is common for young male mountain lions to disperse from their original breeding grounds to look for areas with less competition for food and females. The animal’s necropsy revealed it to be between two and five years old. But Rego said it’s rare that they disperse more than 100 miles.

Previously, the longest documented trip by a mountain lion was 640 miles. But the distance from the first confirmed sighting of the “St. Croix” cat to where its epic journey ended in the northbound lane of the Wilbur Cross Parkway was nearly 1,000 miles.

“This guy had an adventurous spirit,” DEEP Commissioner Dan Esty said.

Rego said that it’s likely the animal traveled from Wisconsin through the southern end of Ontario and then headed southeast to Connecticut. If it had had taken a more southern route it would have come into contact with more urban areas like Chicago, he said.

Right now there’s no way to be sure. Before its death on June 11, the lion was last seen in Greenwich on June 5 when it left droppings that matched its DNA.

DEEP Deputy Commissioner Susan Frechette said a lot of unanswered questions remain.

“We are continuing with both genetic and isotope testing in an effort to determine just how this animal got from Wisconsin to Connecticut. I wish it were here to interview so we could help figure that part out,” she said.

The experts called the mountain lion’s record-setting move to Connecticut an anomaly. Esty assured residents that there is still no evidence of a native breeding population in the state.

But, he said, given that debates in Washington have turned hostile toward environmental efforts across the country, the animal’s appearance here is reason to celebrate.

“We have achieved some real successes in restoring wildlife habitat and ensuring that we as a country are preserving biological diversity and frankly the great natural heritage of our country,” he said.

It’s not clear why it made the trip. The animal must have crossed countless rivers and contended with other obstacles both natural and man-made to get here.

After the press conference Frechette was asked what possible reason the 140-pound cat could have had to come to Connecticut. She said the animal tested negative for rabies, a disease that’s known to cause strange behavior in animals.

She suggested maybe the “St. Croix Mountain Lion” just caught a case of the wanderlust.

“He was a wanderer. He set out east and just kept going.”