After Sirius had resumed his dog form and returned to the forest, Madam Bones returned to Hagrid's hut and asked Hagrid, "Hagrid, may I take the whole jug to the Room of Requirement? I don't want to risk Pettigrew escaping in transit."
"That's fine, Madam Bones," said Hagrid simply.
Madam Bones took the milk jug and walked back up back to the Room of Requirement with a very businesslike mindset.
Once she was inside, she unsealed the milk jug.
The rat tried to escape, but Madam Bones was too quick for him and quickly stunned him.
Madam Bones then quickly fed a few drops of Veritasiurium down the rat's throat and forced Pettigrew into his human form.
Waking Pettigrew, Madam Bones asked, "What is your name?"
"Peter Pettigrew," answered Peter simply.
"Who were your best friends at Hogwarts?" inquired Madam Bones.
"James Potter, Sirius Black, and Remus Lupin," answered Pettigrew.
"Did you support Voldemort and were you at any time a Death Eater?" Madam Bones grilled Pettigrew.
In response, Pettigrew rolled up his left sleeve and showed Madam Bones the Dark Mark.
"Why did you join Voldemort?" Madam Bone asked Pettigrew.
"I thought he could protect me better than my old friends. He had also been gaining power and with the weapons he had he could've killed me if I refused him. It was simply in my best interests to align with the Dark Lord, " answered Pettigrew.
"And were you ever a Secret Keeper?" Madam Bones prodded.
"Yes, " spilled Pettigrew, "Sirius suggested that James and Lily use me as their Secret Keeper. James and Lily chose me as Secret Keeper in the end. I told the Dark Lord where to find the Potters. When the Dark Lord met his downfall, I went into hiding to avoid the wrath of the Dark Lord's followers, who I feared would blame me for his downfall. I framed Sirius by yelling for the whole street to hear that he had betrayed James and Lily and used the Killing Curse to murder twelve muggles. I cut off my finger and used my rat form to escape, thus framing Sirius for my death as well as those of the muggles."
"And what became of you after that?" grilled Madam Bones further.
"I found a wizarding family, the Weasleys, to take me in. I was first Percy Weasley's and then Ron Weasley's pet. But both at the burrow and at Hogwarts I was always keeping an ear out for news. If I ever got word that the Dark Lord had returned, it was always my intent to rejoin him."
"Did Voldemort have a specific plan on how to return?" Madam Bones asked Pettigrew.
"I don't know, " answered Pettigrew fretfully, "But if I ever find out, the Dark Lord can count on me to help him."
Realizing she now had enough to go on, Madam Bones forced Pettigrew back into his rat form and forced him into the jar, reapplying the Anti Breaking Charms to it.