Nouns ending in -elle are usually feminine.
The suffix often forms a diminutive feminine.
Is criminelle masculine or feminine?
lacriminelle
The masculine form is criminel
The rule behind it
95.1% of -elle nouns are feminine
In context
Aucune accusation criminelle n'a été enregistrée.
No criminal charges were filed.
Je ne suis pas une criminelle.
I'm not a criminal.
Ce n'est pas une criminelle.
She's not a criminal.