WHAT IS THE “CHAIN OF CUSTODY” AND WHAT EFFECTS DOES THE BREAKING OF THIS CHAIN CAUSE?
The ATS of February 13th, 2020 pronounces on this matter, which in turn refers to the ruling of the STS (Spanish Supreme Court) second chamber, 747/2015, of november 19th.
This sentence points out that the doctrine has been understanding as "chain of custody" the set of acts that have the purpose of the collection, transfer and preservation of indications or vestiges obtained in the course of a criminal investigation, acts that must complete a series of requirements in order to ensure the authenticity, unalterability and indemnity of the sources of evidence.
The Criminal Procedure Law (LECrim) does not contain a unitary and systematic regulation on the requirements and guarantees of the chain of custody, although it regulates in a scattered manner some aspects related to it, essentially in articles 326 and 334 LECrim.
Likewise, other issues related to the chain of custody are dealt with in arts. 282, 292, 330, 338, 770.3 and 796.1.6, of the LECrim.
The Supreme Court has established in various resolutions two important aspects on this issue:
1) The integrity of the chain of custody guarantees that from the time the traces related to the crime are collected until they become evidence at the time of the trial, they do not undergo any alteration.
As the effects intervened in the course of the investigation have to circulate through different places, it is necessary for the corresponding expert opinions to be issued, to be made sure that what is transferred is the same at all times.
2. The regularity of the chain of custody is a presumption for the evaluation of the piece or element of conviction intervened; in this way, it is ensured that what is analyzed is exactly what is occupied and that it has not undergone any alteration (STS 1072/2012, of 11-12).
This affects the reliability and authenticity of the evidence (STS 1029/2013, of 28-12) and it has also been noted that the rupture of the chain of custody can have an undoubted influence on the violation of the right to the presumption of innocence and to a fair process, since it is necessary to rule out the possibility of the lack of administrative or judicial control of the pieces of conviction of the crime can generate an error on any decisive data related to the criminal trial.
The objections usually made by the parties to the practice of the chain of custody affect matters of a factual nature which, as such, are subject to the general rules on evaluation of evidence.
In other words, the two levels cannot be confused: irregularity in the protocols established as a guarantee for the chain of custody is not equivalent to nullity. It will be necessary to evaluate whether this irregularity (non-mention of any of the data that is obligatory to record; absence of exact documentation of any of the steps...) is ideal to raise doubts about the authenticity or indemnity of the source of evidence.
It is therefore not a question of nullity or unusability, but of reliability (STS 508/2015, of 27-7, among others).