Rule reminder
Passive of perception verbs: 'essere + past participle of perception verb + bare infinitive'. Examples: 'è stato visto uscire' (was seen leaving), 'è stata sentita cantare' (was heard singing), 'sono stati visti aggirarsi' (were seen loitering). The infinitive after the passive perception verb does not change.
The suspect was seen entering the building. → Il sospettato _____ entrare nell'edificio.