What is the effect in a charge of murder if there was no evidence of treachery?

Without evident premeditation, and without any evidence to appreciate the aggravating circumstance of treachery in the killing, the accused can only be held liable as principal for the crime of homicide as defined and penalized under Article 249 of the Revised Penal Code.

Is it a requirement for witnesses to know the names of the assailants?

Witnesses need not know the names of the assailants, as long as they recognize the latter’s faces. What is imperative is that, on the basis of their personal knowledge, the witnesses are positive as to the physical identification of the perpetrators. (People v. Sorila, Jr., 578 Phil. 931 [2008]).

Thus, it was sufficient that the witnesses were able to identify the accused in the crime scene and when they took the witness stand. 

When is there treachery?

There is treachery when the offender commits any of the crimes against persons by employing means, methods or forms that tend directly and especially to ensure its execution without risk to the offender arising from the defense that the offended party might make.

What are the requisites that the prosecution must prove in a murder charge?

For the charge of murder to prosper, the prosecution must prove the following: (1) the offender killed the victim, and (2) the killing was done through treachery, or by any of the five other qualifying circumstances, duly alleged in the Information.  (People v. Gabrino,G.R. No. 189981, 9 March 2011, 645 SCRA 187.)