The story is told in several places, including here. I have no idea if the painting is a forgery, a genuine Caravaggio, a contemporary copy of his work or a genuine painting by some other painter of the same era. But it can be interesting to compare the painting to one on the same topic by Artemisia Gentileschi. Here's the recent find:
And here is Caravaggio's earlier take on Judith beheading Holofernes (left), next to Gentileschi's painting (right) of the same topic:
This quote states what I find interesting about that comparison:
And, most importantly, whereas Caravaggio (above, left) pairs his delicate Judith with a haggard attendant who merely looks on, her eyes wide with disbelief, Artemisia depicts two strong, young women working in unison, their sleeves rolled up, their gazes focused, their grips firm. Caravaggio’s Judith gracefully recoils from her gruesome task; Artemisia’s Judith does not flinch. Instead, she braces herself on the bed, as she presses Holofernes’s head down with one hand and pulls a large sword through his neck with the other. The creases at her wrists clearly show the physical strength required. Holofernes struggles in vain, the thrust of his arms countered by the more forceful movement of Abra, Judith’s accomplice in this grisly act.
The Judith in the first two paintings appears someone who has to be talked into the violence, someone hesitant and maidenly. Gentileschi's Judith is very different. Some argue that it's because Gentileschi's own experience of rape and its consequences. Perhaps. But I also spot a difference which I find hard to name. It's as if Gentileschi's Judith is an individual, someone who has agency, whereas I find the Judith in the other two paintings an almost mythological figure: The passive, virginal maiden who abhors the task she must face.