This is the 10628th most frequent Turkish word.
casuslukla
"With espionage" or "by spying."
In this sentence, 'casuslukla' is used as an ablative case form of 'casusluk', suggesting the topic being referenced (espionage-related).
Casuslukla ilgili filmleri çok seviyorum.
I really love movies about espionage.
Here, 'casuslukla' refers to the act or means of espionage, implying something done in connection with it.
Kendini casuslukla suçlamak gerçekten ağır bir şeydir.
Accusing yourself of espionage is truly a serious matter.
In this instance, 'casuslukla' is used to indicate the object of opposition (espionage), forming an instrumental case role.