Rule reminder
When a causal clause is embedded in reported speech, it follows the same tense-shift rules as other subordinate clauses in indirect speech. If the reporting verb is in the past, the causal clause shifts backward: present indicative → imperfect; passato prossimo → trapassato prossimo (pluperfect). The causal conjunction ('perché', 'poiché', etc.) does not change.
Direct speech: 'Non vengo perché sono stanco.' Reported speech with past reporting verb: 'Ha detto che non veniva _____.'