I witnessed a crime.
as-SIS-tee-toh — the double 's' is slightly longer than in English.
Use when reporting to police that you personally saw an incident. This phrase establishes your role as a witness from the start, helping officers direct their questions appropriately.
'Assistere a' means 'to witness' or 'to be present at', not 'to assist'. This is a false friend for English speakers. Use it confidently when filing a statement at the police station (questura).
Sono stato/a testimone di un crimine.
I was a witness to a crime.
More formal — preferred in official written statements.
Ho visto quello che è successo.
I saw what happened.
Simpler alternative for A2 learners.
C'ero anch'io quando è successo.
I was there when it happened.
Casual — emphasizes your presence rather than your witness role.
Italian police stations are called questure (singular: questura) for the Polizia di Stato and caserme for the Carabinieri. Witnesses give their generalità (personal details) before a formal statement is recorded.