Under international law, a treaty signed by Italy that Italy is obliged to follow, the ECHR judgment is the final word on the legitimacy of Knox's conviction for calunnia against Lumumba. It is up to Italy to find a way to make the status of that conviction conform to the judgment of the ECHR case Knox v. Italy.
Reading the ECHR judgment Knox v. Italy, paragraphs 124 - 139, one will see that the ECHR considers that Knox made officially (ECHR recognized and compliant with Italian law CPP Article 333) complaints at least seven (7) times. Many of these complaints were delivered through her lawyers in official court documents - including appeals and a request for her complaint in court to be transferred for investigation to a prosecutor.
Italy, in its 10 January 2020 communication to the Committee of Ministers of the Council of Europe accepted the ECHR judgment, stated it had paid the Just Satisfaction to Knox, and indicated some very preliminary measures had been taken, primarily the translation of the ECHR judgment into Italian and posting that translation on relevant government and judicial websites for ECHR judgments concerning Italy.
The ECHR judgment includes the facts that Italy did not follow its legal obligations, including under Italian law and ECHR case law, to independently and effectively investigate Knox's complaints of police mistreatment. By accepting the ECHR judgment in its 10 January 2020 communication, Italy acknowledged this by accepting that it had violated Convention Article 3 under its procedural limb.
Italian law enforcement (police and prosecutors) were obliged under Italian law to investigate the complaints (
denuncia or otherwise) they received or became aware of from Knox and/or her lawyers.
Contrary to Italian law CPP Articles 330, 331, 347, and 358, and to the Italian Constitution, Article 112*, the police and prosecutor did not conduct an effective investigation of Knox's complaints of police mistreatment and did not prosecute any individuals who allegedly committed the mistreatment.
* Article 112 states:
The public prosecutor shall have the obligation to initiate criminal proceedings.
Sources:
https://www.quirinale.it/allegati_statici/costituzione/costituzione_inglese.pdf
https://www.brocardi.it/codice-di-procedura-penale/
CPP with explanations (in Italian)
https://hudoc.exec.coe.int/eng?i=DH-DD(2020)27F
Italy's Communication to the CoM 10 Jan 2020