At Proft's command, an ethereal model of the ransacked workshop sprang into being, every detail perfectly recreated. He'd missed something—he knew it—but what?

Reenact the Crime

Exile target nonland card in a graveyard that was put there from anywhere this turn. Copy it. You may cast the copy without paying its mana cost.

Murders at Karlov Manor

"As I suspected, Kylox had prepared a secret exit. But the question remains: Did he escape his assailants or was he taken against his will?"
—Alquist Proft, case notes

Murders at Karlov Manor Promos

If a spell has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

If the spell you cast has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

If you cast a spell "without paying its mana cost", you can't choose to cast it for any alternative costs. You can, however, pay additional costs, such as kicker costs. If the spell has any mandatory additional costs, such as that of Demand Answers, those must be paid to cast the card.

If you don't want to cast the copy, you can choose not to; the copy ceases to exist the next time state-based actions are checked.

You cast the copy while Reenact the Crime is resolving and still on the stack. You can't wait to cast it later in the turn.