I've seen squirrels go up brick, and yes, they've been known to raid nests. But I wouldn't expect a lone squirrel to consume all the babies. It's possible a squirrel, or another bird, raided the nest. Any bits remaining, once on the ground might have been consumed by other birds, squirrels, or cats. Or really, anything that could get to them.

The babies weren't at fledgeling status yet, were they? Even if they were, they don't normally take off in one swoop and not come back, it's a gradual thing. And not the norm for parents to tear apart the nest after that.

Coon raid is a possibility, but I wouldn't expect *that* much activity during daylight. I've seen them come out during the day (it isn't always a sign of illness; sometimes it's just a behavioral adaptation, or it's hot). And they aren't quite as handy scaling a brick wall.

My money'd be on a bird doing the initial damage, after they hit the ground, all bets are off.