About the right to remain silent by the person who is investigated (or accused) in Spanish Law
Article 24.2 of the Spanish Constitution states that: "Furthermore, everyone has the right to the ordinary Judge predetermined by law, to defense and to the assistance of a lawyer, to be informed of the accusation made against them, to a public process without undue delay and with all the guarantees, to use the pertinent means of evidence for their defense, not to testify against themselves, not to confess guilt, and to the presumption of innocence.”
This right is also contemplated in article 7 of Directive (EU) 2016/343 of the European Parliament and of the Council, of March 9th, which reinforces certain aspects of the presumption of innocence in criminal proceedings.
These fundamental rights that are recognized to all investigated or accused, are also reflected in the Spanish Criminal Procedural Law, in its articles 118.1 (for those investigated) and in article 520.2 (for detainees and prisoners).
"Right to remain silent and not to give a statement if you do not wish to do so, and not to answer one or more of the questions that are asked," says the aforementioned article 118 of the Criminal Procedural Law.
“A) Right to remain silent, not testifying if she/he does not want to, not to answer one or more of the questions that are asked, or to state that she/he will only testify before the judge.
"b) Right not to testify against oneself and not to confess guilt", reads article 520.2 of the LECRim.
The Constitutional Court has understood, in various rulings, among others number 161/1997, of October 2nd, that these rights lie at the very heart of the right to a fair trial and are closely linked to the right to the presumption of innocence.
For all of the above, certainly silence cannot be erected in any way as a sign of guilt. A criminal conviction can never be based on the silence of the accused, as this would violate the right to the presumption of innocence.