"He turned back toward me. 'I don't know. I found it. It was in that construction site over across from the mall. In a hole in a wall. Inside the cement block. Like it had been put in there or something.'"
I don't remember a lot about the series. And this question has been on my mind for a few days.
David claims to have 'found' the box in a "hole in a wall. Beside the cement block."
Now, aside from the fact that David is assuming that Marco knows about this very specific "cement block"--it's a construction site, so there must be MANY cement blocks-- I have to say that I don't remember anyone mentioning the fate of the blue box after Elgangor was devoured by Visser Three.
Naturally, the Animorphs would have been too traumatized by the events that occured that night to notice something as small as a blue box, but that still leaves the question of how the box was "Inside the cement block. Like it had been put in there or something," when Elfangor was too busy getting, you know EATEN to put the box anywhere else but the ground at his hooves. And could you hide something INSIDE a cement block?
And, if it was so easy to find this supposed "hidden" block, why didn't the controllers notice the SHINNING BLUE BOX IN A WHOLE IN THE WALL when they were searching the WHOLE construction site after Elfangor was eaten?