The results are in — and they’re potentially terrifying.

Authorities confirmed Tuesday that a snake skin found along the Presumpscot River in Westbrook, Maine, earlier this month came from an anaconda.

“One hundred percent,’’ said Westbrook police Captain Sean Lally, who had a portion of the skin DNA-tested by a herpetologist at a lab in Texas.

The skin, which was found Aug. 20 and was about 12 feet long, had further fueled speculation that a mysterious reptile was living along the stream and feasting on mammals.

While the skin has been identified as that of an anaconda’s, it’s still not clear whether it was placed near the river as a prank, to perpetuate stories of “Wessie,’’ as the quasi-mythical creature has come to be known.

Lally said he doesn’t know what to believe, at this point.

“It could be a hoax, I don’t know. It’s certainly interesting,’’ he said in a telephone interview. “But I don’t know where you find a 10- or 12-foot anaconda skin.’’

Anacondas are native to South America. The largest kind, green anacondas, have been reliably measured at more than 30 feet long, though most do not get more than 16 feet long. They can kill animals by throwing their coils around them or by using their mouth and sharp teeth. They often drag their kills back into the water, according to britannica.com.

Lally said various witness statements about snake sightings, including reports from two officers in his department and a city public services employee, seem consistent with the behavior of an anaconda.

“But again, I don’t know,’’ he said. “It’s a big mystery.’’

Police will continue to work with specialists to strategize ways to locate and capture — or possibly euthanize — the snake, whether or not it’s an anaconda, according to a statement from the department.

The DNA testing and identification was done by John Placyk Jr., an associate professor in the department of biology at the University of Texas Tyler.

Placyk said he reached out to Lally in Maine after he learned through a friend and on social media that the snake skin had been found by the river. Lally agreed to snip a piece of the skin off and send it to Texas.

Placyk said he extracted DNA from the skin and then amplified a mitochondrial gene before comparing it with a national genetic resources database.

When he got a match, his jaw dropped, he said.

“It was pretty unexpected, I’ll tell you that,’’ he said. “This was a 100 percent match to an anaconda.’’

Placyk said the question still remains whether the skin was put there “to mess with people’’ as interest in Wessie has grown.

“The odd thing is that the skin was so well intact, and a lot of times anacondas shed in smaller pieces and it rubs off on branches,’’ he said.

Still, “It is possible there’s one there,’’ he said. “The skin looked pretty fresh to me.’’

He cautioned the public in the area to be vigilant and to not let small pets run loose near the river in the meantime.

Derek Yorks, a wildlife biologist for the state’s Department of Inland Fisheries and Wildlife, said it’s illegal to own an anaconda in Maine. He said it’s “completely possible’’ that someone could have kept one as a pet, however, and then released it into the wild when it grew too large.

“If it’s indeed an anaconda, probably someone didn’t want it anymore and let it go because it was big and required large food prey items,’’ he said. “You’d have to be buying this thing rabbits or chickens.’’

Yorks said it’s also “totally possible’’ that someone in another state, or even in Maine, who has an anaconda illegally, could have brought the skin to Westbrook and placed it out in the woods.

If the snake is real, experts say, it won’t be around for long.

“If there is indeed still a large non-native snake at large in Westbrook, it almost certainly is a tropical or subtropical species that will not survive the winter,’’ Yorks said.

Steve Annear can be reached at steve.annear@globe.com. Follow him on Twitter @steveannear.