The alleged co-conspirator in the Wisconsin school shooting was referred to as ominously “creepy” and “quiet” by current and former California neighbors, according to reports.

An unidentified ex-neighbor from San Diego described Alexander Paffendorf, 20, as “very creepy,” describing how she “never heard him speak a word” despite living next to him and his parents for six years, TMZ reported.

“He looks like someone who would shoot up a place,” she said, adding that neighbors had theorized about him before he was accused of plotting a coordinated attack with Natalie “Samantha” Rupnow, who opened fire at Abundant Life Christian School in Madison on Monday, killing two people and injuring six.

Paffendorf “always had a hood on” and “doesn’t make eye contact,” according to the neighbor.

She mentioned he would follow her closely as she walked down the stairs and had once stood outside her window, despite not uttering a single word. When she confronted Paffendorf’s parents about him lurking outside her window, they blew her off.

“He was very disconnected in his own world,” she said.

Current neighbors also described Paffendorf as quiet and reclusive.

“I’ve only seen him a few times,” the neighbor said. “He’s real quiet, just seen him walk to his car and back, said hello, that’s about it,” Carlsbad resident Alex Gallegos told NBC Philadelphia.

Authorities revealed late Tuesday that Rupnow, 15, had been in contact with Paffendorf leading up to the massacre.

Paffendorf was allegedly planning a mass shooting at a government building in a parallel and coordinated attack with Rupnow, who killed substitute teacher Erin West and freshman Rubi Vergara before turning the gun on herself Monday.

He exchanged messages with Rupnow about targeting a local government building while she shot up the school, according to a gun violence restraining order obtained by CBS 8.

“During an FBI interview, Paffendorf admitted to the FBI agents that he told Rupnow that he would arm himself with explosives and a gun and that he would target a government building,” the two-page emergency restraining order from the Carlsbad Police Department states.

The civil order doesn’t say which building he allegedly planned to strike or details of his conversations with Rupnow.

A San Diego Superior Court judge approved the order under California’s red flag gun law Tuesday night, according to the local California station.

The order required Paffendorf to turn over all his guns and ammunition to police within 48 hours. 

Paffendorf has not been charged with a crime, but a court hearing on the restraining order is set for Jan. 3.

Four days after the school shooting, investigators still have not revealed a motive.