REVEALED: Madison school shooter coordinated attack with California man: FBI

A 20-year-old man in California was recently detained for allegedly plotting to conduct a mass shooting at a government building in the state in conjunction with the school shooting undertaken by 15-year-old Natalie "Samantha" Rupnow in Madison, Wisconsin Monday morning.

According to CBS 8, FBI agents served Alexander Paffendorf, of Carlsbad, with a gun violence restraining order after discovering that he was in contact with Rupnow and had been coordinating an attack on a local government building. The civil action allows officers to seize weapons.

Paffendorf reportedly admitted to the FBI in an interview "that he told Rupnow that he would arm himself with explosives and a gun and that he would target a government building," according to the two-page restraining order from local police obtained by the outlet.

FBI agents reportedly "saw the messages from Paffendorf to Rupnow." The order was approved by a San Diego Superior Court Judge on Tuesday just before 9 pm.

According to the New York Post, Paffendorf was detained. The civil order did not reveal which building he was planning to attack or details of the conversations with Rupnow. The judge approved the order under the state’s red flag gun law, which requires Paffendorf to hand over his firearms and ammunition to officers within 48 hours.

Neighbors of Paffendorf told CBS 8 that over a dozen police arrived at the complex, not long after the order was signed. Alex Gallegos told the outlet, "They had their full guns out all over the street. There were cop cars. I'd say about 15 cops here." He said he saw police carry out a "black gun box" from Paffendorf’s residence.

"I saw them carrying out the big box. I didn't see them arrest anybody, but they gave high-fives as it came to an end," Gallegos said, adding, "It sounds pretty wild and scary that this could happen so close to home."