Chain of custody as means to validate evidence

The Supreme Court has always put emphasis on the importance of the chain of custody as a means of validating evidence, For example, in the recent case of People v. Del Rosario,[1] it was held:
As a method of authenticating evidence, the chain of custody rule requires that the admission of an exhibit be preceded by evidence sufficient to support a finding that the matter in question is what the proponent claims it to be. It would include testimony about every link in the chain, from the moment the item was picked up to the time it is offered into evidence, in such a way that every person who touched the exhibit would describe how and from whom it was received, where it was and what happened to it while in the witness’ possession, the condition in which it was received and the condition in which it was delivered to the next link in the chain. These witnesses would then describe the precautions taken to ensure that there had been no change in the condition of the item and no opportunity for someone not in the chain to have possession of the same.

While testimony about a perfect chain is not always the standard because it is almost always impossible to obtain, an unbroken chain of custody becomes indispensable and essential when the item of real evidence is not distinctive and is not readily identifiable, or when its condition at the time of testing or trial is critical, or when a witness has failed to observe its uniqueness The same standard likewise obtains in case the evidence is susceptible to alteration, tampering, contamination and even substation and exchange. In other words, the exhibit’s level of susceptibility to fungibility, alteration or tampering – without regard to whether the same is advertent or otherwise not – dictates the level of strictness in the application of the chain of custody rule.[2]
In People v. Castillo (G.R. No. 190180, November 27, 2013), the High Court concurred with appellant’s assertion that the arresting officers involved were not able to strictly comply with the procedural guidelines stated in Section 21(1), Article II of Republic Act No. 9165. However, this failed to sway the Court towards granting her absolution because, notwithstanding the procedural error, the integrity and the evidentiary value of the illegal drugs used in this case were duly preserved and the chain of custody of said evidence was shown to be unbroken.[3]

[1] G.R. No. 188107, December 5, 2012, 687 SCRA 318, 330, citing People v. Guru, G.R. No. 189808, October 24, 2012, 684 SCRA 544, 555-556.