Dathan's answer is a dagger.
"Who is he who hath appointed thee a chief man and a judge over us? Wilt thou kill me, said he, as thou didst the Mizraite? And Mosheh was afraid, and said, Verily, the thing has become known."
The Targum Pseudo-Jonathan on Exodus (2:14) puts the sentence into Dathan's mouth with a little extra venom. The sand, it turns out, is a poor confidant. Moses had buried the Egyptian believing he was burying a secret. Dathan is the first to tell him: everyone knows.
And the prophet who yesterday could see an Egyptian's entire future line in one glance cannot, today, see who in Israel is watching him. Prophecy is not a surveillance system. It is a gift given for divine purposes, not for personal protection. Moses can foresee the future of nations and still be surprised that the person he saved is gossiping about him.
"Verily, the thing has become known." Some translators render it indeed, the matter is known. The sages heard a theological tremor in this phrase. Moses is not only saying "my secret is out." He is saying: Now I understand why the redemption is delayed. There is slander among my people. There are Israelites willing to betray other Israelites to Pharaoh. The nation is not yet ready.
It will take forty years of exile in Midian before he is ready to return. It will take four decades more — and Dathan's final rebellion — before Israel is ready to follow him.
Beloved, redemption is delayed not only by tyrants but by the loose tongues of the liberated.