© Elizabeth Robertson/Staff photographer
The FBI arrested Keonna Thomas in April 2015 at her three-story brick-and-stucco rowhouse, on 10th Street near Brown, in the Richard Allen Homes public-housing project.
A North Philadelphia mother of two admitted Tuesday that she planned to abandon her children and travel to Syria to pursue "martyrdom operations" with an ISIS fighter she married over the internet.

Keonna Thomas, 32, pleaded guilty to attempting to provide material support to a terrorist organization during a brief hearing in federal court. She acknowledged her plans were derailed last year only when federal agents raided her home the day she was scheduled to leave the country.

"I believe that I'm guilty of this charge," said Thomas, dressed in a head scarf and green prison jumpsuit, when asked by U.S. District Judge Michael Baylson why she was changing her plea.

Federal authorities had couched the case as the latest in a string of prosecutions to combat what they describe as a "more decentralized, more diffuse, more complicated" homegrown terror threat from U.S. citizens radicalized over the internet.

Since the fall of last year, more than 250 Americans have either traveled to Syria and Iraq or tried to do so in an effort to join ISIS. Nearly 60 were arrested and charged in U.S. courts last year for ISIS-related activities.

But Thomas' decision to admit her guilt just weeks before she was set to take her case to trial came as something of a surprise.

Up until earlier this month, her lawyers - Kathleen M. Gaughan, Elizabeth Toplin, and James J. McHugh of the Federal Defender's Office - were aggressively challenging the government's case in court filings that questioned the tactics used to surveil her and the very charge under which her case had been brought.

Earlier, they had maintained that Thomas was being prosecuted for statements she made on the internet that should be protected under her First Amendment rights.

Gaughan offered little explanation Tuesday for the about-face.

"It was Ms. Thomas' decision after careful consideration of this case," she said. "She's accepted full responsibility for her behavior and conduct. She looks forward to putting this behind her and being a mother to her two young children."

Assistant U.S. Attorney Jennifer A. Williams declined to comment after the hearing.

When and how Thomas became radicalized remains unclear.

Through months of court proceedings, glimpses of her private life emerged, but there was little to explain why she would agree to leave behind 7- and 9-year-old daughters so she could die for ISIS.

As FBI agents arrived at her North Philadelphia house to arrest her in April 2015, they found her cooking breakfast for the children.

Thomas was born in Pittsburgh but came to Philadelphia as an infant. She was raised here, has local family ties, and has lived in the same house with her mother for a decade.

Before her arrest, she had been unemployed for a few years but previously worked as a home health-care aide, like her mother.

According to a plea memo filed Tuesday with the court, Thomas was circulating terrorist propaganda, under the online monikers Fatayat Al Khilafah and YoungLioness, as early as August 2013.

One of her early postings on Twitter pictured a young boy holding weapons. The caption read: "Ask yourselves, while this young man is holding magazines for the Islamic state, what are you doing for it? #ISIS."

Another, posted in April 2014, contained images of a skull, flames, and a gun. Thomas purportedly wrote: "I need a permanent vacation that can only mean one thing." Another Twitter user, court filings say, responded with a word that means "martyrdom."

At some point, Thomas' plans went beyond simply voicing support for terror groups online. She communicated directly with a radical Jamaican cleric, Sheikh Abdullah el-Faisal, and sought his assistance in finding a jihadist to marry.

She later struck up a relationship with Abu Khalid al-Amriki, an ISIS recruit newly arrived in the organization's Syrian headquarters, and married the man in a ceremony conducted over Skype.

When Amriki contacted her in February 2015 to ask whether she was willing to take part in a suicide attack, Thomas responded: "That would be amazing. . . . A girl can only wish."

Thomas has remained in custody since her arrest last year, five days after she missed a flight she had booked to Barcelona, Spain, with plans to travel from there to Syria. Amriki is believed to have been killed last year.

Thomas faces up to 15 years in prison at a sentencing hearing scheduled for Jan. 17.