The first resource I checked after reading your initial comment was the Jewish Publication Society English translation (Tanakh) and the reading there is "Do not deal basely with your countrymen. Do not profit by the blood of your fellow: I am the LORD." The footnote on the expression "profit by" says "Lit. 'stand upon': precise meaning of Heb. phrase uncertain."

Of various versions and commentaries I consulted after that only Barnes Notes alluded to the idea of not standing idly by, he wrote [Stand against the blood of thy neighbor] Either, to put his life in danger by standing up as his accuser (compare Matt 26:60); or, to stand by idly when thy neighbor's life is in danger. Whichever interpretation we adopt, the clause prohibits that which might interfere with the course of justice. (from Barnes' Notes, Electronic Database. Copyright (c) 1997 by Biblesoft)