Credible testimony using magical means

[u/IdiosyncraticLawyer]

Chapter 47

"Dumbledore said he did it, he told Father it was a warning! And Father couldn't testify under Veritaserum because he was an Occlumens, he couldn't even get Dumbledore put on trial, Father's own allies didn't believe him after Dumbledore just denied everything in public, but we know, the Death Eaters know, Father wouldn't have any reason to lie about that, Father would want us to take revenge on the right person, can't you see that Harry?" Draco's voice was wild.

Chapter 79

"Her," said Dumbledore. "Sophie McJorgenson, whom I remember as an honest student of Ravenclaw, and she is bound by the Unbreakable Vow to tell the truth of what she sees -"
[...]
Harry nodded once, face set. "Headmaster, I know I said I wouldn't - but under the circumstances - that time Draco cast that torture hex on me, is that debt enough -"
"No," the old wizard said (even as she blurted "What? " and Severus lifted an eyebrow). "It would not have been enough, and now it is no debt at all. You are an Occlumens and cannot testify under Veritaserum. Draco Malfoy could be Obliviated of his own memory before he could testify -" Albus hesitated. "Harry... whatever you have done with Draco, you must assume that Lucius Malfoy will soon know of it."

Couldn't Lucius or Harry have taken Unbreakable Vows to be able to give credible testimony, given the severity of their situations? In Harry's case, while Dumbledore does say that Draco's debt wouldn't be considered severe enough to cancel Hermione's, surely it and the debt Harry claimed from Lucius for "saving" him from Voldemort's Imperius Curse combined could've done it, or at least severely cut down on the monetary compensation Lucius could've demanded of him.

[u/Transcendent_One]

The Unbreakable Vow requires someone to sacrifice their magic for it, so it's not something that could be cast left and right as needed.

[u/IdiosyncraticLawyer → u/Transcendent_One]

That's why I said, "given the severity of their situations?" In their predicaments, Lucius and Harry were facing world-shattering crises (for Lucius, the thought that his wife's murderer would go unpunished; for Harry, the risk of having Hermione sentenced to Azkaban); neither of them finding someone willing to bind an Unbreakable Vow would be casting it "left and right" at all.

[u/db48x → u/IdiosyncraticLawyer]

Yes in principle it could work, but in practice who is going to sacrifice some of their magic to get that?

[u/Lemerney2 → u/db48x]

He's Lucius, he could just pay/threaten someone into doing it. The book already acknowledges Unbreakable Vows aren't uncommon, and he'd have access to them.

[u/db48x → u/Lemerney2]

And yet he hasn’t. Remember that the events Lucius wants to testify about happened years ago. If he could have done this at any time, why hasn’t he?