A Proper Verita-serum Interrogation
Disclaimer: I do not own the character of Albus Dumbledore, nor the plot devices of veritaserum, obliviation, or pensieves. All Hail JK Rowling.
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"Mr. Dumbledore, you have been charged with several counts of interfering with a recognized House. Because of the severity of your charges, and because of your known tendency to manipulate, obfuscate, and prevaricate, you have been held incommunicado for seven days under a silencing spell. The silencing spell will only be released after you have consumed your dose of veritaserum. You will not be released from custody until after this questioning is complete. Your only way out of this cell is either death, or through questioning."
"Mr. Dumbledore, are you now under the influence of any potions other than veritaserum?"
"Mr. Dumbledore, do you have information that you have sworn a magical oath not to divulge?"
"Please list all the subjects that would cause you to lose your magic were you questioned about them at this time."
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"Is there information that you have sworn, through a verbal or written oath, not to divulge on penalty of losing your life?"
"Please list all the questions that would trigger a penalty of death from your previously sworn oaths."
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"Is any of the information you have sworn not to divulge something that you believe is connected to the inquiry you are undergoing today?"
"In what way might today's inquiry relate to the information you have sworn not to divulge?"
"What questions will reveal as much information as possible related to our inquiry without causing you to lose your life or magic?"
"Have any memories been removed from yourself, through obliviation or pensieve extraction, that relate to the inquiry that you are undergoing today?"
"How can the court retrieve the isolated memories that you have had removed?"
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"Did you knowingly violate the law or custom in placing Harry Potter in the care of his relatives?"
"In what way did you knowingly violate law or custom by placing Harry Potter in the care of his relatives?"
"What were your three primary motivations for violating law or custom by placing Harry Potter in the care of his relatives?"
"Are there other primary motivations that you can honestly confess to that are related to the last question?"
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"What are you attempting to conceal about Harry Potter's placement with his relatives?"
"What do you believe that you have successfully concealed about Harry Potter's placement with his relatives?"
"What relevant factors do you believe that you have led us to disregard about Harry Potter's placement with his relatives?"
"What do you consider to be the most relevant factors regarding your actions in Harry Potter's placement with his relatives that you have not yet revealed?"
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OK – the first questions are to make sure that questioning doesn't inadvertently trigger a magical repercussion like death or squibbing. It moves into forcing the subject to confess in such a way that they do not trigger anything, and then moves onto using their judgment to guide the questioning – and it won't work if the person really believes that they've done nothing wrong.
But usually, humans know when they're guilty, and there really isn't any reason not to use that when the subject is forced to answer truthfully. A quick-and-dirty interrogation is, "What are you guilty of? If I wanted to convict you with the maximum penalty, what charges would I use and what evidence would I use?"
But if the prosecutor wants to avoid the appearance of a 'fishing expedition', this way would uncover it, I think. And this is yet more evidence that JK Rowling does not understand munchkinry.
Which is fortunate, because munchkinry in the real world with that much money could be a serious game-changer.