"Upon discovering Niu Rang, Gu En probably wasn't certain whether it was the Niu Rang from the military, thus Niu Rang was initially tracked and monitored. This made Niu Rang sure that Gu En must have disclosed his identity to Lan Song, and hence he hurriedly left clues for you. That day, once Gu En confirmed that Niu Rang was no longer with the military, it was clear that 'Heizi' was indeed Niu Rang, and Lan Song must have taken action immediately upon receiving the news. Moreover, they must have found the person who delivered items to Niu Rang, and from this person's words, learned that the box contained a dress and a gun. Naturally, everyone believed that the real item Niu Rang meant to give you was the gun, the dress was just a disguise."
"That's why, the night when Niu Rang sacrificed himself, thieves broke into the place where I had just moved in, and by a coincidence, a black replica gun was stolen." If it was Gu En, then everything is clearly explained.
