In procedural law contexts, pieza does not mean “piece,” but rather denotes a “proceeding.” Certain aspects of a case may be adjudicated en pieza separada, i.e., in a separate proceeding from the main trial or proceeding (called pieza principal), and will be recorded in a separate case file (likewise often referred to as pieza separada). In civil proceedings, for example, pieza de medidas cautelares denotes a “provisional remedies proceeding” incident to civil litigation. In criminal procedure, in ordinary felony proceedings (proceso ordinario por delitos graves), a preliminary criminal investigation (instrucción sumarial) is typically conducted in four piezas. In addition to the main investigatory proceeding (pieza principal), a second pieza de situación personal reflects any pretrial measures (medidas cautelares personales) ordered against a suspect (investigado), including arrest (detención), pretrial release (libertad provisional) or pretrial detention (prisión provisional). The remaining two concern civil liability (responsabilidad civil) arising from the commission of the crime in question. The pieza de responsibilidad civil principal contains all measures ordered against the suspect’s property (medidas cautelares reales) to ensure that, if convicted, he will be able to pay the victim the compensation awarded by the court. These may include requiring the accused to make a pretrial deposit into court (prestar fianza) or ordering attachment (embargo) of his property. In the fourth pieza de responsibilidad subsidiaria similar measures may be ordered against third parties who may likewise be liable for civil damages resulting from the offense.
In other respects, the term pieza de convicción refers to the physical evidence of the commission of a crime, defined as objetos inanimados que puedan servir para atestiguar la realidad de un hecho relevante para el proceso.* The expression has sometimes been inappropriately translated as “incriminating evidence,” but whether a pieza de convicción is incriminating or not must subsequently be established at trial.
*Juan Manuel Fernández Martínez, coord. Diccionario jurídico. Thompson-Aranzadi, 2004.