(CNN) -- A New York man pleaded guilty Thursday to three charges over online threats he posted against the creators of the television show "South Park," the Department of Justice said.
Appearing before a Virginia federal court, Jesse Curtis Morton admitted to charges of using the Internet to conspire to solicit murder, making threatening communications and using the Internet to place others in fear.
He faces a maximum penalty of five years in prison on each of the charges when he is sentenced May 18, the Justice Department said in a statement.
Morton was the co-founder in 2007 of Revolution Muslim, a radical group based in New York City that is supportive of al Qaeda's philosophy.
The former Brooklyn resident, also known as Younus Abdullah Mohammad, was taken into U.S. custody in Morocco last May, according to the Justice Department statement.
"Jesse Morton operated Revolution Muslim to radicalize those who saw and heard his materials online and to incite them to engage in violence against those they believed to be enemies of Islam," U.S. Attorney Neil MacBride said in the statement.
"We may never know all of those who were inspired to engage in terrorism because of Revolution Muslim, but the string of recent terrorism cases with ties to Morton's organization demonstrates the threat it posed to our national security."
Morton left the United States in the summer of 2010 because he feared arrest after two associates from New Jersey were charged with terrorism offenses in June of that year, according to a senior U.S. counter-terrorism official.
Investigations had revealed that Revolution Muslim was the "top catalyst for radicalization for violence in the United States" over the last several years, according to the official.
Morton had a multitude of connections to individuals charged or convicted in U.S terrorism cases, the official said.
They included Zachary Adam Chesser, now 21, who last year admitted to posting online threats and attempting to provide material support to Al-Shabaab, a designated foreign terrorist organization.
He was sentenced to 25 years in prison.
Chesser, a Muslim convert like Morton, communicated threats against the writers of "South Park" for an episode that depicted the Prophet Mohammed in a bear suit.
Morton aided Chesser in posting online messages that included the writers' home addresses and urged online readers to "pay them a visit," the Department of Justice said. They also posted speeches by radical Islamist cleric Anwar al-Awlaki giving a justification for killing those who insult the Prophet Mohammed.
In an affidavit accompanying the complaint against Morton, FBI special agent Paula R. Menges said Morton worked with Chesser on a "clarification statement" after the latter's postings.
The pair made website postings that were threats -- despite their claims otherwise, Menges said.
Morton's links with extremists included Samir Khan, the editor of al Qaeda in the Arabian Peninsula's English-language "Inspire" magazine. Khan was killed last September along with al-Awlaki in a U.S. drone strike.
Khan knew Morton from his days living in New York and invited him to contribute to a radical blog he was producing in North Carolina called "Jihad Recollections," before traveling to join AQAP in Yemen in October 2009, according to the official.
Khan told Morton of his plans to travel to Yemen, according to the senior U.S. official. The official was unaware of any communications between the two after Khan left the United States.
Rezwan Ferdaus, a U.S. citizen from Ashland, Massachusetts, who was charged with planning to use model aircraft filled with C-4 plastic explosives in an attack against targets in Washington in September was in touch with Morton as he prepared his operation, according to the official.
Ferdaus asked Morton about the Islamic justification of suicide bombings. Morton replied that what was key was the intention behind them and that they were an enormous benefit in a war of attrition, according to the official.
Morton later invited Ferdaus to speak in more detail in an online conference call he was holding on the website Paltalk. In the e-mails, Ferdaus did not reveal his specific plan, according to the official. Ferdaus has pleaded not guilty to the plot.
Jose Pimentel, a Bronx resident who in November was arrested and charged with plotting to detonate pipe bombs in New York City after allegedly beginning to build an explosive device was in touch with Morton via e-mail before he was arrested, according to the official.
Pimentel wrote that he was big fan of the Revolution Muslim website and "Islam Policy," another website run by Morton, and asked Morton about whether he could trust a particular individual, according to the official. Pimentel has pleaded not guilty to the plot.
Morton's group was connected online to several others who have admitted or been charged in connection with terrorist offenses. Colleen LaRose, an American woman who pleaded guilty last year to conspiring to assassinate a Swedish cartoonist in 2009, was a subscriber to Revolution Muslim's website.
Antonio Martinez, a Hispanic convert to Islam who pleaded guilty to a plot to blow up a Maryland military recruiting station in 2010, also visited the website -- but was not in direct touch with its founders, according to the official.
Abdel Hameed Shehadeh, arrested in Hawaii in October 2010 and charged with making false statements in a matter involving international terrorism, attended Revolution Muslim meetings and made his website a feeder for Revolution Muslim's, according to the official. Shehadeh, who authorities alleged attempted to travel to fight jihad overseas, pleaded not guilty.
Morton's associates in New Jersey were Mohammed Alessa and Carlos Almonte, who last year pleaded guilty to conspiring to murder individuals on behalf of a terrorist group in Somalia. Alessa and Almonte were arrested as they tried to board international flights at a New York airport on June 5, 2010.
A few days later, Morton arranged for tickets to fly to Morocco.
Morton also had a web of international connections, according to officials.
He was in touch with Mohammed Chowdhury, the ringleader of a plot to blow up the London stock exchange and other London targets in December 2010, who pleaded guilty last week.
When Morton moved to Morocco, he asked Chowdhury to take over the running of the Revolution Muslim website, according to the official. Chowdhury was part of a group of radical extremists linked to the British pro-al Qaeda group al Muhajiroun, whose former members have been implicated in several U.K. terrorist plots.
Morton's group Revolution Muslim was a spinoff of the American wing of Al Muhajiroun. The British group is still active in the United Kingdom, operating under different names.
According to the U.S. official, Morton was also in touch with Bilal Ahmad, another member of the same British extremist circle. Ahmad pleaded guilty to soliciting murder after posting a death threat in November 2010 on the Revolution Muslim website against British parliamentarians who had supported the Iraq war.
In a CNN interview in 2009, Morton defended the September 11, 2001, terrorist attacks and argued that further attacks on Americans were justified.
However, he said he did not encourage violence on U.S. soil.
CNN's Drew Griffin and Carol Cratty contributed to this report.