I've found an icloud locked iPhone, how can I return it to the owner?

If the SIM card is deactivated, replace the SIM card with one that is functional and will provide the device with a data connection. This will allow the phone to communicate its location to Find My iPhone which the original owner can use to locate the device.

You can't restore a device with an active Activation Lock (except DFU and that just puts it back in Activation Lock), so “wiping the phone” isn't a possible avenue.

Little know fact is that Apple has a program to return lost devices to the original owner. Bring it to the Apple Store, you get a receipt and Apple should take care of it.

Alternatively if the store is too far away, you can call Apple Support and they'll send a courier over to pick it up on their expense (or give you a shipping tag). This might only be valid in selected countries though; I'm not sure for Brazil.

There is an Apple Store in Rio:

Apple Store Village Mall

Avenida das Américas 3.900

Barra da Tijuca

Rio de Janeiro

RJ 22640-102

PHONE (21) 3179-3700