Everitt Aaron Jameson said he wanted to use pipe bombs to "funnel people into an area in order to shoot them," at Pier 39, according to the federal indictment.
Jameson, 26 of Modesto, California, was indicted on one count each of attempting to provide material support to a foreign terrorist organization, and distribution of information relating to destructive devices, according to court papers.
In a statement to CNN on Thursday, Jameson's federally appointed public defender Charles Lee said his office "will investigate the possibility of an entrapment defense, as well as the government's inability to prove beyond a reasonable doubt any attempted criminal act given Mr. Jameson told the FBI undercover employee 'I also don't think I can do this after all. I've reconsidered.' "
In court papers, Lee said Jameson is mentally ill and didn't have the means to carry out the attack, The Fresno Bee reported Thursday.
The FBI had started watching Jameson in September after becoming aware of social media activity in which he "liked" or "loved" posts about terror attacks and ISIS, according to a federal affidavit written by an FBI agent.
Undercover FBI agents posed as ISIS supporters and contacted Jameson. He met with an undercover FBI employee on December 16 and told them he wanted to conduct the attack using weapons and explosives, the complaint said.
Jameson asked the agent for remote timing devices for the pipe bombs and described how to use the devices in the attack, the indictment said.
According to the affidavit, Jameson said Christmas Day "was the perfect day to commit the attack," which would be styled after the October 31 attack in New York City
in which a man killed eight people when he drove a truck down a bike lane, the affidavit said.
Jameson had said he'd just started working as a tow truck driver, which could help in the attack, according to the affidavit. He expressed loyalty to ISIS and its leader, Abu Bakr al-Baghdadi, and offered to donate money and contribute his firearms skills, the affidavit said.
Jameson asked the undercover agents to get him an assault rifle and explosives and sent them photos of what appeared to be Pier 39, the affidavit said.
Jameson had served in the US Marines in 2009 and attained a sharpshooter rifle qualification. He was later discharged for fraudulent enlistment because he failed to disclose a latent asthma history, the affidavit said.
After several communications on December 18, Jameson appeared to back out, telling an undercover agent, "I also don't think I can do this after all. I've reconsidered," the affidavit said.
Authorities searched his Modesto home on December 20 and found firearms, empty magazines, ammunition and fireworks, the complaint said. They also found a will and a handwritten letter, which said "you've allowed Donald Trump to give Al Quds away to the Jews," in an apparent reference to the President's decision to recognize Jerusalem as the capital of Israel, according to the complaint.
"We have penetrated and infiltrated your disgusting country," the letter said, according to the complaint.
Lee argued authorities didn't find any bomb-making materials in the home. He also said the guns authorities did find belonged to a relative who legally owned them and had locked them in a gun case Jameson couldn't access, The Fresno Bee reported.
Jameson is being held in the Fresno County Jail without bail pending his trial and is scheduled to be arraigned in federal court on Friday, CNN affiliate KPIX