You can look at the original text. Some translations miss nuances in the original language; some interpret the text for or against a particular viewpoint.
And I wouldn't say it's been translated both ways frequently. AFAIK, the only Bible in common use that translates the commandment as "you shall not kill" is the English translation of the Vulgate, which is only one version (albeit a popular version), and it has the problem of being translated to English through Latin instead of directly from the Hebrew.
Also, there can sometimes be another issue (especially with older translations, such as the King James Bible), the English language can change, so our current usage of a word doesn't always match the usage of the word at the time the translation was made. I don't think this is so much an issue for "murder" vs. "kill", but it is an issue for "charity" vs. "love": the 17th Century usage of the word "charity" is closer to our modern definition of "love" than our modern definition of "charity".