Snow has begun falling, so it’s not too early for a Christmas-time detective story: Who really wrote “The Night Before Christmas”?

The poem first appeared, anonymously, in 1823 in an upstate New York newspaper. It soon became a hit. It transformed Santa Claus from a skinny, dour European saint who left nuts and candy for poor children and used a birch rod on bad ones into a jolly old elf with a little round belly that shook when he laughed like a bowl full of jelly.

Thirteen years later, someone attributed the lines to Clement Clarke Moore, a Biblical scholar, a serious poet, and a landowner who was the richest man in America at the time. He modestly disclaimed credit at first. Later, he copied the verses in his own hand and published the poem in a collection of his writings. (One of his hand-written copies was auctioned recently at Christie’s for $255,000.) For more than 150 years, he has been honored as its author and the creator of Santa Claus.

The family of Maj. Henry Livingston Jr., an officer in the Revolutionary War, disagreed. They recalled that old “Harry” had read those lines aloud at a Christmas breakfast in 1808. They were shocked, years later, to see them attributed to Clement Moore. Descendants have searched ever since for the original manuscript or other evidence, but without success.

Enter Don Foster, a professor of English at Vassar, but best known as a literary detective. He consulted ancient family records, old newspaper files, and the known writings of both Mr. Moore and Maj. Livingston, and eventually became convinced that the former was a fraud and the latter the true author. He presents a mass of evidence in a new book, “Author Unknown,” published by Henry Holt and Co.

Maj. Livingston, according to the book, was a lively, fun-loving family man who wrote light-heartedly, whereas Mr. Moore was an old grump, who hated talkative women and noisy children and wrote serious stuff. More to the point, Maj. Livingston often wrote in the anapest beat (da-da-DUM, da-da-DUM, da-da-DUM) while Mr. Moore almost never did. The major often wrote “Happy Christmas,” an unusual phrase in those days. Mr. Foster, after studying Mr. Moore’s writing, concludes, “Moore never said ‘Happy Christmas’ (or ‘Merry Christmas’) to anyone.” The poem originally ended with “Happy Christmas to all, and to all a good night,” although later versions sometimes were changed to “Merry Christmas.”

The false version also messed up the names of the reindeer, says the professor. Instead of Donder and Blitzen, the original called them Dunder and Blixem. That phrase is an ancient Dutch oath (“Thunder and lightning!”), and Maj. Livingston was three-quarters New York Dutch and lived in the Hudson valley, where the names would have come naturally.

That $255,000 manuscript may be losing some of its value, but the poem lives on. And soon the children once again will be nestled all snug in their beds while visions of sugarplums dance in their heads.