Crouch as Moody - the best DADA teacher?

[Jo (Joanna)]

No: HPFGUIDX 170418

I am interested to know what the general opinion is as to why Crouch
as Moody taught the students the unforgiveable curses.

At first I thought it was because he enjoyed torturing the children
whose parents had gone through similar suffering as that of the
spider.

However, why did he tutor Harry until he was able to fight the
curse?  (UK paperback GOF p. 204).

The reasons I can think of are:

1. He wanted to see just how strong Harry was.
2. He enjoyed putting Harry through it with the trade off that Harry
would learn at the same time.
3. He was doing something else to Harry when they all thought he was
using the imperius curse.

Or something else maybe?

Jo.