How can I retrieve Facebook messages?

[Iforgot]

I have a feeling my girlfriend is cheating on me and I got on her fb today & looked through her messages when we were hanging out. She snatched her phone away and deleted those conversations. She doesn't know that I know her password and have it on my phone but I can't prove it until I see those messages with those guys. If there's a way to retrieve them, please let me know. Preferably by phone but if that's not possible then a computer will do just fine. Thank you

[YTMJ]

try checking the archive if there is nothing there, she has fully deleted them and there is no way of getting them back.

[Daniel]

If She Deleted the Messages Than There Gone And There is no Way to Get them Back They would be In the Inbox if your Able to View Them

By the Way Get Out of Her Account Hacking is Not Legal and is Wrong if you Get Caught you Can Get Into Some Trouble