A Las Vegas security guard has been charged after bomb-making materials were found in his home and he promoted white supremacist ideologies online, the Department of Justice says.
Conor Climo, 23, had been discussing attacking a synagogue and "conducting surveillance" on a bar he believed catered to the LGBT community.
A notebook was found allegedly containing plans for attacks.
In 2016, he made local news for walking the streets with an AR-rifle.
"If there is possibly a very determined enemy, we at least have the means to deal with it," he said at the time.
Mr Climo was charged with one count of possession of an unregistered firearm, which the US Department of Justice stated was being used for the component parts of a destructive device.
Investigations found the security guard had been in contact with white supremacists.
"Climo was communicating with individuals who identified with a white supremacist extremist organization using the National Socialist Movement to promote their ideology," a statement by the Department of Justice said.
"He discussed attacking a Las Vegas synagogue and making Molotov Cocktails and improvised explosive devices, and he also discussed conducting surveillance on a bar he believed catered to the LGBTQ community."
A notebook found in his house contained sketches of timed explosive devices.
Mr Climo - who could get up to 10 years in prison and a $250,000 fine - also attempted to recruit a homeless man to carry out "pre-attack surveillance" on at least one Las Vegas synagogue and other targets, the statement said.
This is not the first time concerns have been raised over Mr Climo.
When he was 20, local news outlets reported how he was patrolling streets in Centennial Hills armed with a rifle and knife, claiming that he'd had enough of crime in the area.
"I don't know what his intentions are, what his motives are, what his background is," one neighbour told KTNV.
There have been more than 250 mass shootings in the US this year. Last weekend, mass shootings in Dayton, Ohio, and El Paso, Texas, left more than 30 people dead.
The suspect accused of killing 22 people in El Paso, has confessed that he was targeting "Mexicans".