A teenager allegedly killed his parents as part of a plot to assassinate US President Donald Trump, federal authorities say in newly unsealed court documents.

The alleged killing of his parents appeared to be an effort to attain the “financial means and autonomy” to carry out his plan, investigators said.

Casap faces nine felony charges, including two counts of first-degree murder and two counts of hiding a corpse, according to the Waukesha County court docket.

His mother, Tatiana Casap, and his stepfather, Donald Mayer, were both found dead inside their home from gunshot wounds. Authorities believe they were killed on February 11. The WaKeeney Police Department in Kansas initially arrested Casap for stealing his stepfather’s SUV and possessing a firearm.

The Waukesha County Sheriff’s Office obtained a search warrant and found material on Casap’s phone related to the “The Order of Nine Angles”, which is “a network of individuals holding new-Nazi racially motivated extremist views”, according to court documents. They also found photos and communications referencing a self-described manifesto regarding assassinating the president, making bombs and terrorist attacks, according to investigators.

In the vehicle, the sheriff’s office found an open safe, women’s jewellery, electronics, about $US14,000 ($22,000) and banking documents.

A three-page document the FBI found called for Trump’s assassination to create a political revolution in the US and “save the white race”.

“As to why, specifically Trump, I think it’s pretty obvious. By getting rid of the president and perhaps the vice president, that is guaranteed to bring in some chaos,” one excerpt from the document said, according to the affidavit.

The document also contained images of Adolf Hitler along with the text: “HAIL HITLER HAIL THE WHITE RACE HAIL VICTORY.”

The FBI additionally found an image and messages on his phone with information on how to use a drone as an attack drone, according to the documents. He paid, at least in part, for a drone and explosives to commit an attack, investigators said. They had also found photos of the front and back of Mayer’s credit and debit cards, and the username and password of a bank account.

The 17-year-old’s classmate told the sheriff’s office in March that Casap had told him he planned to kill his parents but did not have access to a gun, according to the affidavit.

Casap later told the classmate that he would befriend someone who had a gun and steal it, according to the affidavit. The court document also said Casap told his classmate that he was in contact with someone in Russia and they were planning on overthrowing the US government and assassinating Trump.

Casap is scheduled to appear for arraignment on May 7, according to the Waukesha County court docket.