Answer
The difference lies in whether the offender performed all the acts of execution. In a frustrated felony, the offender has done everything that would produce the crime, and only an independent cause — not the offender's own doing — prevents the result (the classic example is a mortal wound from which the victim survives only because of timely medical intervention). In an attempted felony, the offender has begun the crime by overt acts but has not completed all the acts of execution, and the crime is left incomplete by some cause or accident other than his own voluntary desistance.
For crimes against persons such as homicide, the Supreme Court applies the subjective-phase test: if the wound is mortal and the victim survives only through medical assistance, the crime is frustrated; if the wound is not fatal, it is only attempted. If the offender voluntarily desists before completing the acts of execution, there is no attempted felony, though he may still be liable for whatever acts already committed amount to another offense.
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