The concept is, make animation with transparency in the middle of the composition, export using PNG sequence, bring the pngs back into after effects, make the layers 3D, make all the layers 24 frames, create an opacity animation from 100 to 0 on all the layers, use Animation > Keyframe Assistant > Sequence layers to overlap the layers 23 frames, add a throw expression to the position so its throwing in the z direction, add a point light with 150 shadow darkness, 100 shadow dif, add another ambient light, and finally make sure all the pngs have cast shadows on in the material options.... done...
veloc = 1000;
x = position;
y = position;
z = position + (time - inPoint) * veloc;