(CNN) A synagogue and a Georgia pipeline were the targets of two Ohio residents arrested by federal authorities in separate investigations, officials said on Monday.

Authorities said Damon Joseph, 21, planned to kill worshipers inside a Jewish synagogue in Toledo with an assault rifle. In a second case, Elizabeth Lecron, 23, is accused of purchasing bomb-making materials she intended to use to blow up a pipeline.

Both arrests followed monthslong investigations in which clues, such as images of guns or words of support for mass murderers, were posted on social media.

The stark difference in Joseph and Lecron's targets shows the scope of the challenge for investigators, said Justin E. Herdman, US attorney for the Northern District of Ohio.

"It's not just one threat. It's across the spectrum," Herdman told CNN in an interview on Monday. "It's not just Islamic or anarchist or animal rights terrorism. It's everything."

Investigators became aware of Joseph after they noticed pictures of knives and firearms on his social media accounts, court records show. FBI agents posing as members of ISIS began a monthslong conversation with Joseph in which he offered his services in creating propaganda videos, court records show.

Joseph would routinely talk online with undercover agents who he thought were members of ISIS, the records show. The conversations ranged from details about his propaganda videos to his beliefs, and he admitted he struggled with the idea of killing but was not afraid to go to prison, since he would be able to recruit fellow inmates. Then in September, the agents asked Joseph if he hated people in America. "Oh yeah, definitely," answered Joseph, according to court records. "The gays the Christians the Catholics the Jews you name it."

Undercover agents later met Joseph in person and were given a shopping list of weapons and ammunition, items he needed to mimic the October Tree of Life shooting , where 11 people were killed, Herdman said. On his list was an assault rifle, semi-automatic pistol, at least two magazines and ammunition, according to the indictment.

By the time Joseph met with undercover agents on Friday, they said, he had fine-tuned his plot. Joseph had narrowed his plot to one synagogue and showed one of the agents pictures from inside the structure, saying he wanted to start the killing spree in the sanctuary, records show. Joseph, who also wanted to make sure he killed a rabbi, said he was going to raid the synagogue on the Sabbath so he would cause maximum bloodshed, records show.

Later that day, agents sold Joseph two inoperable AR-15's and that is when they took him into custody, records show.

"This guy is one firearm away from another Tree of Life shooting. That's what he wanted to do," Herdman said. "He was clear on what his intent was and what his plan was."

Joseph's attorney declined to comment.

Tip, social media posts lead to another suspect

Meanwhile, investigators were tipped off months ago by a resident about Lecron, who gushed on social media over mass murderers like Columbine High School shooters Eric Harris and Dylan Klebold, and Dylann Roof, the man who killed nine people in a 2015 massacre at a historically black Charleston, South Carolina, church.

Lecron, who attempted to send Nazi literature to Roof, told undercover FBI agents she hatched a murder plot for a Toledo bar. She then decided to target a livestock farm and wanted to form a team, officials said, before changing course again and saying she and her roommate planned to make a pipe bomb and were gathering materials.

Earlier this month, Lecron told an undercover agent she was considering a pipeline in Georgia. She agreed to buy black powder needed to make the bomb and had bought hundreds of screws, intended to be used as shrapnel in the blast, at a sporting goods store on Saturday, records show.

Information on Lecron's attorney was not immediately released.

"The longer these people are in place on the street the greater the risk is that they're going to kill somebody," Herdman said. "It was just the right time to take them down."

Another man, Vincent S. Armstrong, 23, was charged Wednesday with providing false statements to a law enforcement officer, federal and local authorities said. Armstrong, who lives with Lecron, has been in custody since Monday.

According to an affidavit filed in Armstong's case, he and Lecron flew together in August to visit locations related to the mass shooting at Columbine. Authorities searched their home in August and found several weapons, including an AK-47, a shotgun, handguns and ammunition, along with end caps that Armstrong purchased, which can be used to build pipe bombs, according to the affidavit.

Authorities also found journal entries by the couple discussing a violent attack. "Now I have these thoughts. ...These memories. They haunt me. I have a vision. A vision to kill. To hunt the unwilling. These peasants to society," Armstrong wrote on June 8, according to authorities.

In an interview Monday with authorities, Armstrong denied discussing the attack plans with Lecron and purchasing items that could be used to make a bomb, according to the affidavit. That day, authorities found a duffel bag in the trunk of Armstrong's car with several items, including a tactical vest with two loaded magazines for an AK-47 and printouts of instructions of how to build various bombs, according to the affidavit.

CNN has not determined whether Armstrong has an attorney.