The arrest of Julian Assange at London is a positive development that should hasten the day when the founder of Wikileaks will be brought before an American court. He was seized on a U.S. extradition warrant. An indictment, for a conspiracy related to computer hacking, has now been unsealed. His prosecution will be a teaching moment for America, Mr. Assange himself, and the press that collaborated with him.

Existence of the American extradition warrant was first confirmed by the Metropolitan police at London. Officers arrested Mr. Assange inside Ecuador’s embassy after the government at Quito ended the sanctuary to which Mr. Assange fled a warrant for rape at Sweden. Officers carried the bearded and unkempt Mr. Assange head first out of the embassy as he raved about how the U.K. must “resist.”

Mr. Assange had always maintained that what he feared was not the rape case in Sweden (the Swedes dropped it) but the prospect of extradition to America, against which Wikileaks has been operating for years. Developments today provide the first official glimpse of the nature of the charges. They are sketched in an indictment unsealed in United States District Court for the Eastern District of Virginia.

What strikes us is the allegation that Mr. Assange’s — and Wikileak’s — role was far from passive. That is a contrast to what we, for one, perceived to be the concept of Wikileaks, supposedly a passive online receptacle up to which anyone could load secrets while maintaining their anonymity. That is different from the charges against Mr. Assange as they can be glimpsed in indictment unsealed today.

America alleges that between January and May 2010, Mr. Assange conspired directly with an American GI, Private Manning, in an effort to encourage and assist the soldier in uploading secrets onto the Wikileaks site. Manning, America alleges, uploaded four databases that contained something close to 750,000 documents, including battlefield reports and State Department cables.

It was a shocking breach of our country’s wartime secrets. There was, it seems, nothing passive about it. Manning has already been convicted in the case, drawing 35 years and serving seven before being released by President Obama. America charges that Mr. Assange entered into an agreement with Manning to assist the soldier with attempts to crack a Defense computer password.

“During the conspiracy, Manning and Assange engaged in real-time discussions regarding Manning’s transmission of classified records to Assange,” a Justice Department press release summarizes. “The discussions also reflect Assange actively encouraging Manning to provide more information.” At one point Mr. Assange told the private: “Curious eyes never run dry in my experience.”

When sentenced, Manning had expressed remorse. Yet today, despite Mr. Obama’s commutation, the private is back in prison, this time for contempt for refusing to testify in the Wikileaks case. The private is appealing, according to the Washington Post. Manning’s attitude and Mr. Assange’s own comportment raise the prospect of a long slog for the prosecutors, who deserve America’s gratitude.

We say that having spent our entire career trying to find out what our government is up to, often trying to get government officials — from selectmen to senators, from privates to presidents — to share information. Yet we are horrified at the nihilism displayed by Wikileaks. It’s hard to think of a scoop that would have been worth the crime. We’d like to think that a trial of Julian Assange would put all this in the true light of day.