פאלעקס,
קנאפער איז גערעכט. וואס דו טענהסט אז מ'נוצט רויבער פאר גניבות, דאס אמאל פאר'ן שם פעולה (אויך נישט עמטליך). אבער שם דבר איז אייביג א גנב.
For instance, a theft is always something that was stolen. A robbery is always something that was robbed. There's a robber and there's a thief. Robbers will go to the bank in middle of the day when it's open and rob with force by using weapons or threats to take the money themselves or force others to give it to them.
Thieves will break in to the bank at night when it's closed and take what they want while no one is there. If they encounter resistance, such as a security officer, they would either stop their thievery and run away or if they attack the guard then they become robbers.
Thief, theft, robber, robbery are all nouns. They are always used in the correct way. However, the verbs 'rob' or 'robbed' are also used when thieves commit a theft. So, yes, when someone swindled money he 'robbed' them but the criminal still remains a thief not a robber, and the crime still remains a theft and not a robbery. Technically, the correct way is to say he 'stole' from them, but occasionally it's more dramatic or easier to say robbed.
Also, when you say this item was 'stolen' it would "technically" have to be through thieves commiting a theft, and when you claim an item was 'robbed' it has to be through robbers. But the verb 'stolen' is still used more often. For instance, "this is a stolen item" or "this item was stolen" vs "this is a robbed item" or "this item was robbed" the latter is not grammatically accurate.
So, nouns: always stay true, verbs: sometimes swing both ways (why, I do not know)
גזלן = רויבער
גנב = גנב/דיב