Gay US soldier Bradley Manning, headed to trial on Monday, where military prosecutors said he “systematically harvested” secret documents to share with anti-secrecy site Wikileaks.

After being in captivity for 1,100 days, Manning headed to Fort Meade to face trial on Monday, where his defence argued that he was young and naive when he shared the documents.

He does not deny the part he played in sharing the documents, and could face life in prison if he is found guilty.

In February Manning pleaded guilty to 10 of the 22 charges against him but denied the most serious charge against him – aiding the enemy. He claimed that he had shared the documents to spark debate around the US military, and foreign policy.

Prosecutors have argued that he endangered American lives and national security.

He was nominated for the Nobel Peace Price in March for having “fueled democratic uprisings around the world”.

On Monday, Captain Joe Morrow said it was an example of a case ”when arrogance meets access”.

“This, your honour, this is a case about a soldier who systematically harvested hundreds of thousands of documents from classified databases and then dumped that information on to the internet into the hands of the enemy,” he continued.

The prosecution argued that he had used his military training to gain notoriety, and that he had attempted to hide what he had done throughout the process.

Manning’s lawyer David Coombs said he was “young, naive and good-intentioned” when he first arrived in Iraq, but that he had become disillusioned when he saw an Iraqi person die, and he had seen colleagues celebrating that no US soldiers had been hurt.

“He believed this information showed how we value human life,” Coombs said, arguing that he had been “selective” with the information he took.

“He was troubled by that. He believed that if the American public saw it, they too would be troubled.”

The prosecution opened with arguments relating to the most serious charge made against him – aiding the enemy. For Manning to be found guilty, the prosecution must prove that he did just that, and that he knowingly divulged information to US adversaries.

One of the leaked videos from Manning showed footage of an Apache helicopter attack back in 2007, which killed twelve people in Baghdad, including a photographer from Reuters.

His trial is expected to run all summer, and whatever prison sentence receives, is to be reduced by 112 days, after a judge previously ruled that he had suffered unduly harsh treatment during his initial arrest.

At the weekend, activists gathered around the world to support Manning. In London around 250 people gathered at the US Embassy, including human rights campaigner Peter Tatchell and fashion designer Vivienne Westwood.