What about in the New Testament? "You have heard the commandment,'An eye for an eye, a tooth for a sooth.' But what I say to you is: offer no resistance to injury. When a person strikes you on the right cheek, turn and offer him the other." (Mt.5:3-40)
The whole of that is "an eye for and eye, a tooth for a tooth, and A LIFE FOR A LIFE" here clearly Jesus is saying, no there are no stipulations on Thou Shalt not kill.
Also in John 8, the adultress by the Law of Moses as you stated above, the woman should have been killed, but Jesus said, "whosoever has no sin, let him cast the first stone."
Other bibilical references against Euthanasia can be in the case of King Saul (I Samuel 31:1-6), who was mortally wounded in the battle against the Philistines; he begged for his own armorbearer to kill him rather than to allow him to die slowly in torture or suffer humiliation from the enemy who would take him captive. Saul attempted suicide when his orderly refused.
Later (II Samuel 1:1-10), an Amalekite from a neutral nation passed by and Saul begged him to take his life. Stand beside me and slay me for anguish has seized me and yet my life still lingers (verse 9). His response was exactly that of the practitioner of euthanasia. So I stood beside him and slew him because I was sure that he could not live after he had fallen (verse 10). What happened? God condemned it!
The Amalekite was killed for his act, but why? David described the act as putting forth the hand to destroy (II Samuel 1:14). From his judgment we seemingly must conclude that it was completely unacceptable to God, regardless of the motive behind it. David equates the Amelakite's act with an act of assassination and we are left to assume that he reflected the Biblical stance of the sacredness of life and the importance of preserving it