As military prosecutors wrapped up their case against Bradley Manning just before the Fourth of July, their most serious charge against the Army private first class - aiding the enemy - rested tenuously on circumstantial evidence.

The government began building its case in the wake of Manning's June 2010 arrest. Criminal investigators and forensics experts swooped in to figure out how a low-level intelligence analyst stationed in a remote corner of Iraq could send thousands of files - on subjects ranging from the State Department to Guantanamo - to WikiLeaks.

Prosecutor Capt. Joe Morrow said in his opening statement that the investigation concluded "Pfc. Manning knew the consequences of his actions and disregarded that knowledge in his own self-interest."

Despite the three years it took to bring Manning to trial, government investigators have not been able to turn up any smoking gun to prove that Manning knew the leaks would wind up in the hands of those such as Osama bin Laden. Instead, the prosecutors lowered the bar dramatically, arguing that Manning is guilty of the aiding the enemy charge because he knew that al Qaeda has access to the Internet, and to WikiLeaks in particular.

On one level, it is a simple matter of common sense that al Qaeda has Internet access. The group publicly posts videos and messages online. And it seems just as obvious that al Qaeda officials would visit the WikiLeaks page from time to time, just as they would read Twitter, The New York Times or Al Jazeera.

The government's argument, then, is that any member of the military who leaks classified information with the knowledge that it will be posted on the Internet is aiding enemies of the United States. Under that reasoning, even civilian senior White House officials who regularly share classified information with top journalists could perhaps be charged with aiding the enemy - a charge punishable by death, although prosecutors have not sought that sentence for Manning.

Texas Tech University law professor Richard Rosen said that to convict Manning of aiding the enemy, the government "must prove that Manning knowingly gave intelligence information to the enemy. In other words, it must show something more than Manning should have known that the intelligence might reach al Qaeda. It may, however, show actual knowledge by circumstantial evidence."

Bit by bit, tweet by tweet, the government has been trying to build up that case - but the almost entirely circumstantial evidence makes it far from clear as to whether they will succeed. In a move made public Monday, Manning's defense lawyer motioned to have the aiding the enemy charge dismissed for lack of evidence.

Between Morrow's June 3 opening statement and when the prosecution rested on Tuesday, the government brought out a parade of supervisors and trainers to testify that Manning was told al Qaeda and other foreign adversaries use the Internet to gather knowledge.

Manning underwent more than a year of training before he was deployed to Iraq. But based on the evidence presented in trial, it appears he was never specifically told that al Qaeda might use WikiLeaks - either as a propaganda tool or an intelligence resource.

Did Bradley Manning know the files he gave to WikiLeaks would also wind up in Abbottabad? The government has been endeavoring to show that Manning had "evil intent." That dramatic-sounding phrase appears in Judge Denise Lind's pre-trial instructions to the parties about the aiding the enemy charge. She wrote that the government will need to prove that Manning had "evil intent" to convict him of aiding the enemy.

But the phrase may not be as damning as it sounds: University of Pittsburgh visiting law professor David Frakt cautioned as the trial was starting that those words are "being used simply to denote wrongfulness, as opposed to a purely innocent intent."

Showing evil intent is where Manning's own understanding of putting files on WikiLeaks, rather than just anywhere on the Internet, really comes into play, Frakt said. Evil intent means the government will need to show "the accused had to know he was dealing, directly or indirectly, with an enemy of the United States [via WikiLeaks]," he said.

Proving Manning coordinated with WikiLeaks, and didn't just use it as a simple receptacle to dump documents for his own reasons, is crucial to the prosecution's larger case on the aiding the enemy charge. They want to show that Manning knew what would happen when he gave the transparency organization his many files.

And that took the trial to two tweets by WikiLeaks in early 2010. The timeline of those tweets is in dispute. But the prosecution suggests that in each case, Manning downloaded sensitive government files after seeing the WikiLeaks tweets: one, seeking video of a devastating Afghanistan airstrike that killed civilians, and the second, requesting a list of as many military email addresses as possible.

A government prosecutor said in a brief that the tweets show WikiLeaks had a "plan to compromise military information" - a plan Manning knew about.

Yet the government can't prove that Manning ever actually saw those tweets. In its brief asking the judge to allow them as evidence in the case, the government pointed out that the law allows it to "meet its burden of proof with direct or circumstantial evidence."

Over the three and a half weeks of its case, the government repeatedly sought to meet the burden of proof with the latter: circumstantial evidence. The aiding the enemy charge has always been controversial, but now that the government's case has been laid out in full, the seeming reliance on circumstantial evidence is further infuriating critics.

Jesselyn Radack, who has defended National Security Agency whistleblowers in her work at the non-profit Government Accountability Project, calls the charge "excessive prosecution at its worst."

"It's a huge stretch to apply this to Manning," she said, "and the theory the government is using to prove it is downright frightening."