NEW YORK (CBSNewYork/AP) — Two women caught in a 2015 terrorism sting involving an undercover NYPD officer posing as an Islamic convert pleaded guilty on Friday to charges they studied how to make bombs for a terrorist attack on U.S. soil.

Noelle Velentzas and Asia Siddiqui, both from Queens, admitted in federal court in Brooklyn that they had looked for recipes for homemade explosives on the internet and shopped for components at Home Depot with the intent to bomb government targets. Both women made passing references to a third person who was in on their plans – a woman they knew at the time only as “Mel.”

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Noelle Velentzas (left) and Asia Siddiqui (right) appear in U.S. District Court on charges of plotting terror in 2015. (Credit: CBS2)

Velentzas and Siddiqui were arrested at their Queens homes following a sting operation using an undercover officer wearing a wire. Officers searching the homes recovered items including three gas tanks, a pressure cooker, fertilizer, handwritten notes on the recipes for bomb making and jihadist literature, court papers said in 2015.

Authorities had revealed in court filings that the third woman known as “Mel” was an undercover counterterrorism officer who befriended the terrorist duo while the officer was assigned to mingle with young Muslims around the city to identify potential threats.

Velentzas was “obsessed with pressure cookers since the Boston Marathon attacks in 2013,” and was caught on recordings made by the undercover in 2014 ranting against the United States and saying she and Siddiqui were “citizens of the Islamic State,” prosecutors said in court papers. When the women were arrested, investigators discovered propane gas tanks, soldering tools, jihadist propaganda and machetes in their homes, they said.

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“In an effort to implement their violent, radical ideology, the defendants studied some of the most deadly terrorist attacks in U.S. history, and used them as a blueprint for their own plans to kill American law enforcement and military personnel,” stated U.S. Attorney Richard Donoghue said in a statement on Friday.

The pleas ended the prospect that the women’s trial would provide a rare glimpse into how the NYPD uses informants and undercovers to smoke out Islamic extremists – a method long criticized by civil rights groups who say it risks luring harmless people into phony plots. Police officials had expressed concern that the officer’s cover could have been blown if she had to testify.

Prosecutors say Velentzas and Siddiqui face up to 20 years in prison but the term could be shorter under sentencing guidelines and with credit for the more than four years they’ve already been behind bars awaiting trial.

Velenzas will be sentenced on Dec. 5 and Siddiqui on Dec. 18.

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