(CNN) -- Jihadist social media postings helped lead to the arrest and charging of four Los Angeles area men, who were allegedly on their way to Afghanistan to train with the Taliban and join al Qaeda, federal officials said.
They were also plotting to kill American soldiers and bomb government installations, according to a joint statement Monday by the FBI and the U.S. Attorney in Los Angeles.
One of the men, a U.S. citizen born in Afghanistan, encouraged two of the others to embrace violent Islamic doctrine by introducing them online to radical teachings, including those of deceased U.S.-born al-Qaeda imam Anwar al-Awlaki.
The three exposed their connection to each other and their radical leanings explicitly on Facebook for over a year. And one of them detailed his intentions to participate in jihad in an online chat with an FBI employee.
Another man was recruited at a later point to join the other three in their training.
All four were charged Monday in a federal court in California, where three of them appeared for the first time. One of the men was already in Afghanistan, where he was also apprehended, said U.S. attorney André Birotte Jr. and assistant director Bill Lewis from the FBI's Los Angeles Field Office in a joint statement.
Sohiel Omar Kabir, Ralph Deleon, Miguel Alejandro Santana Vidriales and Arifeen David Gojali face charges of supporting terrorists who conspired to kill, kidnap or harm U.S. officers and other U.S. citizens, as well as bomb public places and government facilities.
The Joint Terrorism Task Force in Riverside, California, arrested Deleon, 23, Santana, 21, and Gojali, 21, on Friday. Kabir, 34, is in custody in Afghanistan, according to the criminal complaint submitted to the U.S. District Court.
Kabir spent six months in Germany before arriving in Afghanistan last July, where he was preparing for the others' arrival.
The 74-page complaint details evidence collected against the men from online chats with FBI employees, travel documents, extensive contact with an informant, recorded conversations and their active social media accounts.
Kabir, Santana and Deleon all posted radical jihad content to their Facebook page, the court documents allege. But Kabir's page in particular contained multiple links to and videos by al-Awlaki, videos depicting mujahideen fighters in Afghanistan, improvised explosive devices and suicide bombings.
"Deleon and Santana 'liked' postings on Kabir's Facebook page as early as May 2011," according to the court document.
Kabir led Santana and Deleon to convert and join the Taliban, eventually leading to membership in al-Qaeda, the criminal complaint alleges. Santana recruited Gojali, the fourth man, to join them for the trip abroad to train as terrorists.
Santana tipped off authorities about his militant inclinations when a customs officer at the border with Mexico questioned him about the jihad magazine "Inspire" he was carrying into the United States.
He allegedly engaged in chat conversations with an FBI "online covert employee" and confirmed his desire to join al Qaeda.
An unnamed "confidential source" working for the FBI won the trust of Santana and Deleon, according to the complaint, spent time with them and recorded many of their conversations.
"Santana and Deleon told a confidential source...that they planned to travel to Afghanistan to engage in "violent jihad," the FBI and U.S. Attorney statement said.
Their conversations with the confidential source revealed details of their "travel logistics, including flights, passports and visas." Kabir was to meet up with the three others and lead them to the Taliban, the court document said.
Santana and Deleon allegedly pre-trained on a firing range and at a paintball center and took the confidential source along with them.
Deleon told the confidential source he would quit school and withdraw his tuition money to help pay for the trip to Afghanistan, the criminal complaint said.
Santana told the confidential source said he would like to drive a truck bomb, if he could do it with a big truck. "Just drive it into like the baddest military base," he said, according to the document. "If I'm gonna do, I'm gonna do that. I'm gonna take out a whole base."
Kabir is a naturalized U.S. citizen, who was born in Afghanistan and lived in Pomona, California. Deleon is a permanent U.S. resident living in Ontario and was born in the Philippines. Santana, a resident of Upland, is a lawful permanent resident, born in Mexico, who has applied for U.S. citizenship. Gojali, 21, of Riverside, is a U.S. citizen.
The men face a maximum sentence of 15 years in a federal prison, if convicted.
CNN's Irving Last contributed to this report