system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] Why don't they use the/a Pensive to get witness testimony to resolve issues?

After the final defeat of You Know Who, the wizarding world at large was shocked to learn any number of truths that had been concealed by both the ministry and Albus Dumbledore for many reasons. Here are a few examples:

1. The innocence of Sirius Black and truth behind the betrayal and murder of James and Lily Potter.

2. The veracity of Harry Potter's claims during his 4th year of You Know Who's second rise to power and the events during the Triwizard Tournament.

3. Claims by former/renounced Death Eaters after the first and second fall of You Know Who.

Why did the suspected or disbelieved parties not volunteer or be requested to produce their memories to be examined through the Pensieve? Even if it is a unique magical artifact produced by Albus Dumbledore, there seems to be very little way to tamper with it or use it to convey false or altered memories without the alteration being obvious, and it is possible for the memories of people other than Albus Dumbledore to be shown, as demonstrated by Harry Potter's testimony of his examination of Horace Slughorn's altered memories during his 6th year. The first example above seems like it would have produced a swift acquittal for Sirius Black had he presented his memories of the Secret Keeper Binding ceremony involving Pettigrew or his confrontation with Pettigrew, and Harry Potter could easily have shown precisely what happened in the cemetery at Little Hangleton and proved the true loyalties of many supposedly "renounced" Death Eaters. Even if it is considered taboo or an invasion of privacy, surely the benefits to the suspected/disbelieved outweighs the cons?

Edit: I apologize for the misspelling in the title. I spelled it correctly in the rest of the post at least...
gpt
Slughorn altered his memory. As Dumbledore said, it was clumsily done, and it shows that it had been altered. If wizards were considering committing a crime, they would just research methods of concealing their true memories and they'd do it properly.