Vixen is not correct. There are not two categories of suspect. You are a witness or you are a suspect in Italian law, but we really don't need to be detained by Italian law because the ECHR trumps it:
If you're a suspect you get a lawyer. It's that simple. However, there is no cause of action if you are not prosecuted or if your prosecution does not rely on the product of your lawyerless interrogation. If you do not incriminate yourself, nobody arrests you and nobody prosecutes you, there is no trial and you are not adversely affected by any theoretical rights violation. Rights are "practical and effective". (See below).
The key case law is Salduz v Turkey: Everything changed in Europe after this.
"52. National laws may attach consequences to the attitude of an accused at the initial stages of police interrogation which are decisive for the prospects of the defence in any subsequent criminal proceedings. In such circumstances, Article 6 will normally require that the accused be allowed to benefit from the assistance of a lawyer already at the initial stages of police interrogation. However, this right has so far been considered capable of being subject to restrictions for good cause. The question, in each case, has therefore been whether the restriction was justified and, if so, whether, in the light of the entirety of the proceedings, it has not deprived the accused of a fair hearing, for even a justified restriction is capable of doing so in certain circumstances.
53. These principles, outlined in paragraph 52 above, are also in line with the generally recognised international human rights standards … which are at the core of the concept of a fair trial and whose rationale relates in particular to the protection of the accused against abusive coercion on the part of the authorities. They also contribute to the prevention of miscarriages of justice and the fulfilment of the aims of Article 6, notably equality of arms between the investigating or prosecuting authorities and the accused.
54. In this respect, the Court underlines the importance of the investigation stage for the preparation of the criminal proceedings, as the evidence obtained during this stage determines the framework in which the offence charged will be considered at the trial (Can v. Austria, no. 9300/81, Commission's report of 12 July 1984, § 50, Series A no. 96). At the same time, an accused often finds himself in a particularly vulnerable position at that stage of the proceedings, the effect of which is amplified by the fact that legislation on criminal procedure tends to become increasingly complex, notably with respect to the rules governing the gathering and use of evidence. In most cases, this particular vulnerability can only be properly compensated for by the assistance of a lawyer whose task it is, among other things, to help to ensure respect of the right of an accused not to incriminate himself. This right indeed presupposes that the prosecution in a criminal case seek to prove their case against the accused without resort to evidence obtained through methods of coercion or oppression in defiance of the will of the accused (see Jalloh v. Germany [GC], no. 54810/00, § 100, ECHR 2006-..., and Kolu v. Turkey, no. 35811/97, § 51, 2 August 2005). Early access to a lawyer is part of the procedural safeguards to which the Court will have particular regard when examining whether a procedure has extinguished the very essence of the privilege against self-incrimination (see, mutatis mutandis, Jalloh, cited above, § 101). In this connection, the Court also notes the recommendations of the CPT (paragraphs 39-40 above), in which the committee repeatedly stated that the right of a detainee to have access to legal advice is a fundamental safeguard against ill-treatment. Any exception to the enjoyment of this right should be clearly circumscribed and its application strictly limited in time. These principles are particularly called for in the case of serious charges, for it is in the face of the heaviest penalties that respect for the right to a fair trial is to be ensured to the highest possible degree by democratic societies.
55. Against this background, the Court finds that in order for the right to a fair trial to remain sufficiently "practical and effective" (see paragraph 51 above) Article 6 § 1 requires that, as a rule, access to a lawyer should be provided as from the first interrogation of a suspect by the police, unless it is demonstrated in the light of the particular circumstances of each case that there are compelling reasons to restrict this right. Even where compelling reasons may exceptionally justify denial of access to a lawyer, such restriction - whatever its justification - must not unduly prejudice the rights of the accused under Article 6 (see, mutatis mutandis, Magee, cited above, § 44). The rights of the defence will in principle be irretrievably prejudiced when incriminating statements made during police interrogation without access to a lawyer are used for a conviction.’"