The case of "Jihad Jane" -- the middle-aged woman from suburban Philadelphia linked to an alleged plot to kill a Swedish cartoonist held to have insulted the prophet Mohammad -- represents the worst nightmare of US security authorities: a white, female, all-American terrorist.
More details have emerged of 46-year-old Colleen LaRose, accused by federal prosecutors in Pennsylvania of conspiring on the internet with overseas-based militants to murder the cartoonist Lars Vilks, proclaiming herself ready to help Muslims and if necessary to become a martyr for the cause of radical Islam.
The picture is of a woman who spent much of her time alone at home on the computer.
But although she seemed slightly odd to some of her neighbours and had few friends in the area, her boyfriend yesterday said that she never gave any clue of pro-Muslim sympathies, and never attended religious services before she abruptly moved out of his flat in August 2009.
"I came home and she was gone, it doesn't sound like the person that I knew. She was a good-hearted woman," Kurt Gorman, who makes radio station equipment, said.
But two months after vanishing without trace, Ms LaRose -- who used the online aliases of "Jihad Jane" and "Fatima LaRose" -- was arrested in October in Philadelphia. The case was kept under seal until Tuesday afternoon, when prosecutors unveiled the indictment against her. No further court dates have yet been set.
If convicted on the charges of treason, she could be sent to prison for life, as well as facing a fine of $1m. But it was not clear last night exactly how serious a threat Ms LaRose posed in reality. She is not identified with any major terrorist organisation. Prosecutors nonetheless insist she was part of a genuine and dangerous conspiracy.
Most alarming perhaps is the fact that she fits no common terrorist profile. Ms LaRose is white, with blonde hair and green eyes. She was born in Michigan, moved to Texas and then to the Philadelphia area. "It shatters any lingering thought that we can spot a terrorist based on appearance," Michael Levy, the US prosecutor for eastern Pennsylvania, said.
According to government officials, "Jihad Jane" had targeted Mr Vilks after he had infuriated Muslims by depicting the Prophet with the body of a dog.
She is said to have had online discussions about how to kill him with at least one of seven suspects who were arrested in Ireland on Tuesday.
Those detained were two Algerians, two Libyans, a Croatian, a Palestinian and an American woman married to one of the Algerians.
The indictment says that from mid-2008 Ms LaRose, using her aliases, began posting messages on the internet saying she wanted to help Muslims.
By early last year, she was allegedly in contact with other as yet unidentified conspirators in Europe and South-east Asia, when she declared herself willing to die for an Islamic cause.
In turn these individuals apparently suggested that she take advantage of her blonde appearance and American passport to travel to Sweden to carry out a murder.
Ms LaRose agreed, promising that "I will make this my goal until I achieve it, or die trying".
Later she tried to raise money online to finance the project.
Shortly afterwards she came to the notice of the US authorities, who took her in for questioning by the FBI in July 2009.
But according to the indictment she lied to agents, telling them she had never tried to raise money, had never used the alias "Jihad Jane," and had never posted messages on a terrorist website.
In August she travelled to Europe, carrying Mr Gorman's passport which, the indictment says, she planned to give to one of her new-found "brothers" to enable him to move to Europe as well. But although Ms LaRose searched online to find her intended target, Mr Vilks, prosecutors say that she does not appear to have actually tried to commit the crime.
Only two women have faced US charges of terrorism-related offences. But neither were involved in conspiracy plots as elaborate as that of which Ms LaRose is accused.