The Scouts worry over the thought of Titan spies in their midst as Commander Erwin makes attempts to extract the Female Titan’s human form. However, the Female Titan uses a scream to attract nearby Titans which devour its body.
Erwin worries that the human pilot has escaped in the steam. When the Scouts are ordered to retreat, a cloaked figure approaches Squad Levi in the air, killing Gunther.

You can watch Attack On Titan Episode 20: Erwin Smith: The 57th Exterior Scouting Mission, Part 4 online for free in the next link:

PART 1

PART 2

PART 3

PART 4

PART 5