Flight to Evade Apprehension

A and B, both store janitors, planned to kill their employer C, at midnight and take the money kept in the cash register. A and B together drew the sketch of the store, where they knew C would be sleeping, and planned the sequence of their attack. Shortly before midnight, A and B were ready to carry out the plan. When A was about to lift C's  Mosquito net to thrust his dagger, a police car with sirens blaring passed by. Scared, B ran out of the store and fled, while A went on to stab C to death, put the money in the bag, and ran outside to look for B. The latter was nowhere in sight. Unknown to him, B had already left the place.

What was the participation and corresponding criminal liability of each, if any?

There was an express conspiracy between A and B to kill C and take the latter's money. The planned killing and taking of the money appears to be intimately related as component  crimes, hence a special complex crime of Robbery with Homicide. The conspiracy being expressed, not just implied, A and B are bound as co-conspirators after they have planned and agreed on the sequence of their attack even before they committed the crime. Therefore, the principle in law that when there is conspiracy, the act of one is the act of all, already governs them. In fact, A and B were already in the store to carry out their criminal plan.

That B ran out of the store and fled upon hearing the sirens of the police car, is not spontaneous desistance but flight to evade apprehension. It would be different if B then tried to stop A from continuing with the commission of the crime; he did not. So the act of A in pursuing the commission of the crime which both he and B designed, planned, and commenced to commit, would also be the act of B because of their expressed conspiracy. Both are liable for the composite crime of Robbery with Homicide.

Alternative Answer;

A shall incur full criminal liability for the crime of Robbery with Homicide, but B shall not incur criminal liability because he desisted. B's spontaneous desistance made before all acts of executions are performed, is exculpatory. Conspiracy to rob and kill is not per se punishable.

The desistance need not be actuated by remorse or good motive. It is enough that the  discontinuance comes from the person who has begun the commission of the crime but before all acts of execution are performed. A person who has began the commission of a crime but desisted, is absolved from criminal liability as a reward to one, who having set foot on the verge of crime, heeds the call of his conscience and return to the path of righteousness.