Photographing himself at Ground Zero proclaiming a perverse sort of victory was a loathsome but clearly protected form of free speech by Tarek Mehanna.

It was when Mehanna’s anti-American thoughts turned to actions — when he traveled to Yemen to seek terrorist training, when he translated and disseminated on the Internet documents promoting jihad — that his First Amendment claims essentially fell apart. That was the distinction made yesterday by a federal jury, which convicted Mehanna on terrorism-related charges.

Jurors didn’t buy the defense claim that Mehanna, who was raised in Sudbury, was simply a devout Muslim who sought further education in Yemen, who expressed controversial but protected personal views on the Web.

Instead they put stock in the testimony of his former associates — that the purpose of the 2004 trip to Yemen was in fact “to go to war.” They had Mehanna’s voice, captured in an FBI recording, expressing fear that the true purpose of the trip would be detected by authorities, and acknowledging that, well, he didn’t go to Yemen “to graze goats.”

The fact that this young American pharmacist never fired a weapon, never planted a roadside bomb, has inspired critics to argue his actions did not amount to crimes.

But conspiracy — in this case, conspiracy to kill Americans overseas, and to provide material support to terrorists — is a crime for a reason. Preventing acts of terrorism is a solemn duty of the U.S. government, and a jury has now determined that Mehanna crossed the critical line between word and deed.