The guilt of Trotsky depends on the jurisdiction in which he is tried and their interpretation of the necessary elements of Felony murder. Typically one is guilty for the actions of his fellow agents in a crime. However, in the instance that an agent goes off on a "frolic of his own," not significantly connected with the crime, Trotsky would cease to be guilty for the actions within the "frolic." Trotsky's guilt for Lenin's slitting of throats would be up to the fact finders deciding if Lenin was on a "frolic of his own." Most likely he would find that Lenin's actions were significantly disconnected from the original crime to be considered separate.

In order to be convicted of Felony Murder the jurisdiction would also have to prove that the felony was "inherently dangerous." There are two ways to analyze this. The "abstract method" being a look at the face of the predicate felonies statute. If this felony is dangerous per its definition(i.e. kidnapping, or rape) then it is considered inherently dangerous. But if the crime is not dangerous on the face of its statute, or can be done "nicely," then it is not inherently dangerous and hence cannot be a predicate felony. The other analysis is the "as committed" test. In which case the crime is analyzed as to the particulars of how it was committed and a decision is made from there. In the abstract case Trotsky walks. In the as committed only the fact finder could tell us, my guess would be this crime would suffice given that a death resulted.

This is a pretty academic answer but brings some other points worth considering to light. It is not nearly as cut and dried as the previous posters supposed.