Last year, FBI agents and undercover operatives watched as Lionel Williams, 27, of Suffolk, Virginia, revealed plans to help Islamic State militants in Syria and Iraq, as well as plans for an attack against the U.S. homeland.

Last month, Williams pleaded guilty in federal court to attempting to provide material support to the Islamic State, also known as ISIS, a designated foreign terrorist group, and will be sentenced in December.

His case will be discussed as part of a seminar, “16 Years After 9/11: The Current Status of Islamist Terrorism,” on Sept. 8 at The Heritage Foundation.

Williams’ plot brought the total number of Islamist terrorism plots and attacks against the U.S. homeland since 9/11 to 97. Chronologically, Williams’ was the 94th plot since 9/11, but since his plot was foiled three additional plots have been uncovered or carried out, making the total 97.

In March 2016, a former associate of Williams tipped off the FBI that Williams was posting ISIS materials on his Facebook page and that he had purchased an AK-47-style rifle the day after the deadly December 2015 terrorist attack in San Bernardino, California.

Local police reported that Williams had been practicing with the rifle near his home.

An FBI agent then contacted Williams through Facebook, pretending to be a radical Islamist. Williams then met with an undercover agent, stating that he supported attacks on “hard targets,” likely referring to police or military targets.

Williams stated that the only reason he hadn’t already carried out an attack was because he was caring for his grandmother.

Williams said he wanted to provide funding to ISIS in the meantime. Through multiple undercover agents, he sent $250 to an individual he was led to believe was working for the Islamic State. He thought the money purchased a rocket-propelled grenade launcher and ammunition.

While he was funding ISIS, Williams continued to discuss a “martyrdom operation,” or attacks at home that would result in his death. He believed that unless he had something to live for, his attack might not be pure, and his death would be considered a suicide rather than martyrdom.

To solve that problem, he arranged a marriage to a woman outside the U.S., which led him to conclude that after he married her, “the next time I see her will be in [heaven].” He went on to say he was planning to send the rest of his money to ISIS so that he would die without a dollar to his name.

With Williams clearly moving toward an attack and already in possession of firearms, the FBI arrested him in December 2016.

On Aug. 16, he pleaded guilty to charges of attempting to provide material support to ISIS and will be sentenced on Dec. 20. He faces up to 20 years in prison.

>>> Join The Heritage Foundation on Sept. 8 for a discussion on the state of Islamist terrorism around the world.

As we approach the anniversary of 9/11, the U.S. must remain vigilant to the threat of Islamist terrorism.

With the decline of ISIS in Syria and Iraq, the number of terrorist plots in the U.S. have fallen substantially. In 2015, the U.S. faced 17 Islamist plots and attacks; in 2016, 13. So far in 2017, the U.S. has faced only three.

It should go without saying that what happens outside America’s borders does not necessarily stay there. The violent ideology of Islamist terrorist groups drives many to fight for their cause, especially when these groups appear to be having success or when they are allowed to plot and plan from the safety of a chaotic region.