Killing a Living Being

In buddhism, killing of a living being is sinful, if

• The party will be killed is a living being
• The person who is killing should be aware the party which will be killed is a living being
• The killer should intentionally do the killing
• Eventually, the object should be killed.

See how logical it is , in law also almost all the above conditions should be met in order to sue him against a first degree murder. Buddhist think all leaving beings are equal, and animals are not "introduced" to the world in order to serve human, and sacrifice their lives whenever humans need. I may not be correct in that way. You can argue. Again think of a case where a person goes to the butcher and buy meat. Will that not be a SIN then?