In this week's episode of Commissario Manara, Lara and Luca are having a romantic walk on the beach, but Lara isn't very tranquilla (relaxed and unworried). She worries about the others at work finding out about their relationship. Luca tries to lighten things up a bit, to sdramatizzare (to remove or reduce the drama or seriousness).
The word they volley back and forth is some form of sospettare/sospetto (to suspect/suspicion). As in English where we have different forms of the word, Italian has them, too, but not exactly as in English. Let’s have a look at what Lara and Luca say to each other.
E poi qualcuno comincerà a sospettare.
And then, someone one will start to suspect.
Rubino, un sospetto senza una prova rimane un sospetto.
Rubino, a suspicion without proof remains a suspicion.
Te lo devo insegnare io?
Do I have to teach you that?
E io ho il sospetto che sto per cederti di nuovo.
And I have the suspicion that I'll give in to you again.
E io ho la prova.
And I've got the proof.
Captions 18-22, Il Commissario Manara - S1EP9 - Morte in paradisoPlay Caption
In the above example Lara starts out with the infinitive verb form sospettare (to suspect), then Luca answers using the noun form un sospetto (a suspicion/a suspect). He may have been playing with the words, since what he said could also have meant: "a suspect is just a suspect unless there is proof." Lara plays with words, too, but, instead of conjugating the verb sospettare, she uses the noun form il sospetto (the suspicion) with the verb avere (to have): Avere il sospetto (to have the suspicion).
Below is an example of the verb form sospettare in the second person plural:
Voi sospettate di me?
Do you suspect me?
Ma vi ho chiamati io? -Si calmi signora Brumelt,
But I'm the one who called you! -Calm down, Missus Brumelt,
Captions 46-47, Il Commissario Manara -S1EP5 - Il Raggio VerdePlay Caption
Note that sospettare is both transitive and intransitive and may take a preposition as in the above example, where di (of) is the preposition, indicating an indirect object. It can also take a direct object, or no object at all.
The adjective sospettoso (suspicious) describes a person who has a suspicious or mistrustful nature (Marika gives us an example here).
An adjective describing something or someone that arouses suspicion is sospetto(suspicious), as in the following example.
Niente, c'è un giardiniere sospetto nel vostro giardino,
Nothing, there's a suspicious gardener in your garden.
mi ha chiesto di fare una verifica.
She asked me to run a check.
Captions 47-48, Il Commissario Manara - S1EP6 - Reazione a CatenaPlay Caption
Someone who is suspected of something may be un sospetto (a suspect) or sospettato (suspected).
Stanno interrogando un sospetto.
They're questioning a suspect.
È sospettata di aver ucciso suo marito.
She's suspected of having killed her husband.
To sum up:
Depending on the context, the word sospetto may have the following meanings:
Noun: il sospetto (the suspicion), il sospetto (the suspect)
Conjugated verb in the first person singular: sospetto (I suspect)
Adjective: sospetto (suspect or suspicious)
The verb sospettare is both transitive and intransitive.
The past participle sospettato is used in the passive voice (as in the above example) or as a normal past participle.
Let the context be your guide. It's a little tricky to get right, but the good news is that while the meaning and use may vary slightly, the sense of the word is basically the same as in English. Little by little, through reading and listening, you'll get a feel for how it's used in context.