[Octokiddie]

E = mc^2

Consume a small amount of mass, release a very large amount of energy due to the huge conversion factor. The first law isn't violated because the energy being released is coming from the annihilation of matter.

Mass and energy can in principle be converted given the right process. LLNL consumed the mass that produced the energy.

[nailer]

Dumb question but why does the velocity of light come into it? I understand how mass stores energy but never got the velocity of light part.

[TchoBeer]

The short answer is that it's a unit conversion factor. Physicists often work in units where c = 1, and then the equation becomes E=m multiplied by a unit conversion term.

[Udo]

If you imagine (rest) mass to be a special form of energy to begin with, you're already 99% there. The fact that the speed of light squared is used as a conversion factor is superficially due to the way our units system is constructed, and in a deeper way it is due to the fact that fundamental properties of the universe are reflected in all of its fundamental processes (so, in a way these are also conversion factors in the actual mechanics of the universe).