Lawyers produced logs of online chats they claim showing his apparent 'role' in the theft of secret military documents, The Daily Mail reports.
The prosecutors made the allegations in an hour-long presentation at Manning's pre-trial hearing for allegedly uploading 700,000 stolen documents to WikiLeaks.
They disclosed three new excerpts taken from Manning's personal laptop.
In one, he allegedly asks Assange for help in figuring out a password. In another, he tells him, 'I'm throwing everything I've got on at you now' and estimates the 'upload is about 36 percent' complete.
According to the paper, the prosecutors claimed Manning, 24, used the online alias of 'Nobody' while talking to 'Nathanial Frank' which they claim was an alias for Assange.
In one chat, Manning asked 'Frank' for help cracking the password on his classified computer so he could log on anonymously.
He asked if he had experience breaking such 'hash' codes. 'Frank' allegdly replied yes they had 'rainbow tables' for doing that.
Assange has denied direct contact with Manning, but his lawyers believe the evidence produced in the military court would form an espionage conspiracy case against their client.