star wars - Why did the Empire need Luminara Unduli’s corpse?

In Star Wars: Rebels (“Rise of the Old Masters”), Kanan and Ezra go in search of Jedi Master Luminara Unduli, whom they believe to have survived and to be in Imperial custody. They discover what they believe to be her, but is actually a hologram.

It is revealed to be a trap by the Grand Inquisitor:

INQUISITOR: Yes, I’m afraid Master Luminara died with the Republic. But her bones continue to serve the Empire, luring the last Jedi to their ends.

_{Star Wars: Rebels, “Rise of the Old Masters”}

What purpose did Unduli’s remains serve? The trap apparently consisted of false messages and a hologram, and the hologram was arguably not even necessary, only serving to get Kanan and Ezra into a certain room.

Why did the Empire need her body? Why did they use it as part of the trap?

Answer

Showrunner Dave Filoni spoke to this in an interview with IGN. In short, the combination of her physical remains and her Force presence due to her death in the holding cell create a weird mix of essence and presence that feels odd, but is still sufficiently attractive to would-be Jedi rescuers.

Filoni: Literally, what you see in that hologram, is her sitting, waiting to be executed. It’s a recording of that event. So when they walk in and see her, they’re actually standing where the Inquisitor was standing [when it was recorded]. And so when she walks up and looks at them kind of distantly and not very friendly, she’s looking at the Inquisitor and that’s what the recording is of. Then she steps over into that chamber and obviously she gets killed there. It’s really wicked when you think about it. The material of her body is the essence that Kanan is somehow sensing through the Force. But he knows there’s something off about it. But since he didn’t really know Luminara, he doesn’t really know. That’s one of the interesting things about death and then the dark side and all these different ways you can use the Force. The sensing of people is one of the biggest dilemmas, I think, in all of Star Wars, because people want to use it like a metal detector.

_{^{STAR WARS REBELS: DAVE FILONI ON THE LUMINARA TWIST IN "RISE OF THE OLD MASTERS"}}