Ba'al ha'Turim: The fact that it is common to find a corpse during wartime.

Sotah, 45b and Sifri: It implies that it is an unusual occurence to preclude where (the corpse is found on the border of the country or close to a town of Nochrim - Sotah, Ibid.), where murder is common, and by the ssame token, Eglah Arufah only applies when murder is uncommon. ¹

Yerushalmi, Sotah, 9:1 #1. It implies that the corpse is easily found - to preclude where it was hidden and required a search to find it. ²

Yerushalmi, Sotah, 9:1 #2: "Ki Yimatzei" implies via witnesses - who testify that the found corpse fulfils all the necessary requireents. Refer to 21:1:2:1.

Sotah, 44b and Yerushalmi, 9:2: A Chalal is someone who was killed - and is no longer shuddering ¹ - by the sword, but not if he was strangled ² (or cast down from a high place - Yerusalmi, Ibid). ³

Targum Yonasan and Sotah, 44b: "ba'Adamah" - precludes where the corpse is found buried underneath a pile of stones; ¹ "Nofeil" - where it is hanging on a tree ² , and "ba'Sadeh" - where it is floating on the water - which are all not subject to the Din of Eglah Arufah.

Yerushalmi Sotah, 9a: It precludes Chutz la'Aretz from the Din of Eglah Arufah. ¹

Sifri: It incorporates Eiver ha'Yarden in the Din of Eglah Arufah. ²

Sotah 45b: To preclude Yerushalayim - which was distributed among the tribes - from the Din of Eglah Arufah. ¹

Sotah, 44b: "Nofel", 've'Lo Taluy be'Ilan'; ¹ "ba'Sadeh", 've'Lo Tzaf al'P'nei ha'Mayim' "Chalal" however, incorporates 'Mushlach' ? if it has been cast on the ground.

Sotah, 47b and Yerushalmi Sotah, 9:1: It implies that if even one witness knows the identity of the murderer - even if he lives at the other side of the world (and even if that person is an Eved Cana'ani or a Shifchah Cana'anis - Yerushalmi Sotah, 9:1) - they do not bring the Eglah Arufah. ¹