BURDEN OF PROOF IN CRIMINAL CASES:

     When an accused invokes self-defense, the burden of proof to show that the killing was justified shifts to him.  Even if the prosecution evidence may be weak, it could not be disbelieved after his open admission owing authorship of the killing.  However, to implicate a co-accused as a co-principal, conspiracy must be proven beyond reasonable doubt.  In the absence of conspiracy, the responsibility of the two accused is individual, not collective. Otherwise stated, when the accused invoke self-defense, the burden of proof is shifted to them to prove that the killing was justified and that they incurred no criminal liability therefor.  They must rely on the strength of their own evidence and not on the weakness of that of the prosecution, for even if the latter is weak, it could not be disbelieved after their open admission of responsibility for the killing. (People vs. Tan, G.R. No. 132324, September 28, 1999, Panganiban, J.).