Usaamah Abdullah Rahim, the terrorism suspect who was killed by police in Boston, abandoned a plot to behead the organizer of a controversial "Draw Muhammad" competition in favor of killing police officers, law enforcement sources told NBC News on Wednesday.
Rahim, 26, was killed Tuesday morning after he was stopped for questioning. The FBI said Wednesday that Rahim was the subject of a terrorism investigation into an alleged plot to kill law enforcement officers sometime this week.
The law enforcement sources said Rahim chose that course only after he worked on plans to travel to New York and behead Pamela Geller, executive director of the American Freedom Defense Initiative, an organization classified by the Southern Poverty Law Center as an anti-Islam hate organization.
Geller was host of a "Draw Muhammad" contest last month in Garland, Texas, that ended with police killing two gunmen outside the event.
"They targeted me for violating sharia blasphemy laws. They mean to kill everyone who doesn't do their bidding and abide by them voluntarily," Geller told NBC News by email Wednesday night. "This is a showdown for American freedom. Will we stand against this savagery, or bow down to them and silence ourselves?
"It won't end with me or the cops," Geller added. "It's just beginning. The one thing that's being ignored that came out of Garland is that ISIS is here. Islamic terrorism is here."
The FBI said in an affidavit filed in connection with charges against David Wright, an alleged co-conspirator, that Wright and Rahim abandoned the Geller attack plans because Rahim couldn't "wait that long."
Instead, Rahim decided to target police officers — calling them "the boys in blue" — and intended to start killing them either Tuesday or Wednesday, the FBI said.
Law enforcement sources told NBC News that the alleged plot to kill police was more believable than the alleged plot to behead Geller, which one official described as a "fantasy."
"We don't know whether they even knew where to find her," another source said.
Wright, 24, also known as Dawud Sharif Abdul Khaliq, was arrested Tuesday night and charged with conspiring with Rahim to destroy evidence of the alleged plot. The FBI said that evidence was Rahim's smartphone, which carried records of calls between the two men and text messages in which Rahim described his plots in guarded language.
Rahim had been under investigation and surveillance for several weeks by the Boston Joint Terrorism Task Force, according to the FBI affidavit. A senior official told NBC News that officers were investigating whether Rahim had become radicalized by ISIS-inspired social media messages and that they feared a terrorist plot was in the works.
Shawn Henry, a former assistant director of the FBI in charge of criminal investigations and cyber-investigations, said the ISIS network's use of social media remains one of the biggest recruitment tools for them and other groups hoping to gain a foothold and following in the West.
"Those who have been inspired historically through the web are now being bantered by social media, Twitter, etc.," Henry said on TODAY, "and it's causing huge concern for law enforcement and the FBI."
This article originally appeared on NBCNews.com.