He feels a great deal of remorse and sorrow for what he did.

But sorry is the Kool-Aid of human emotions. [...] True sorrow is as rare as true love.

If you know someone who tries to drown their sorrows, you might tell them sorrows know how to swim.

I can't believe you are showing no remorse.

He has expressed great remorse over that. He's remorseful that he didn't say anything.

High minds, of native pride and force, Most deeply feel thy pangs, Remorse; Fear, for their scourge, means villains have, Thou art the torturer of the brave!