It is possible to add a telegram-account to multiple devices. We added Telegram Messenger to a MacBook. This created a possibility for us to intercept messages from an other user including the chat history.  During the installation you need to add your phone number and enter the code that is sent by sms to you.
Some phones will, depending on your settings, show the code in the sms even if a phone is locked by a pin-code. This gives us the opportunity to get Telegram-data from an other user as long as we have acces to his/her phone for a brief moment. After entering the code on your computer, Telegram immediately pushes the chat-data to your computer, including sent pictures.


The other user of the same Telegram account will be notified about this action, but at that moment it is already to late to prevent your messages to be confiscated by “some other party”