The man suspected of stabbing five people at a rabbi's house in New York state on Saturday kept journals which included references to Jews and anti-Semitism, authorities said.
Federal prosecutors have filed hate crime charges against Grafton Thomas over the attack.
The filing says his journals included drawings of the Star of David.
His internet search history also included questions such as "why did Hitler hate the Jews", it said.
Grafton Thomas's attorney pointed to his client's history of mental health problems, and said there is no evidence the attack was driven by anti-Semitism.
There has been an increase in police patrols around Jewish neighbourhoods and synagogues following the attack.
What was found in the journals?
The criminal complaint said agents recovered journals from the suspect's home in Greenwood Lake, New York, including comments such as "why [people] mourned for anti-Semitism when there is Semitic genocide".
It says the 37-year-old also used his phone to search for "why did Hitler hate the Jews" on four occasions.
"German Jewish Temples near me" and "prominent companies founded by Jews in America" were also searched, along with other references to "Nazi culture" and swastikas. On Saturday, Grafton Thomas accessed an article about an increase in police presence in New York after possible anti-Semitic attacks.
He is expected to appear in federal court on Monday to face five counts of obstructing the free exercise of religious beliefs by attempting to kill with a dangerous weapon and causing injuries.
What did his lawyer say?
Michael Sussman, Thomas's lawyer, told a press conference on Monday that he had requested a full mental health evaluation.
"We were able this morning to... review scores of papers which frankly show the ramblings of a disturbed individual, but there is no suggestion in any of those ramblings... of an anti-Semitic motive," he told reporters.
How did the attack unfold?
A man brandishing a machete on Saturday attacked a Hanukkah celebration at the rabbi's property in Monsey - an area with a large population of ultra-Orthodox Jews.
Rabbi Yisroel Kahan, who was in the house at the time, described the moment the attack began.
"He pushed his way in, slammed the door shut and said 'none of you getting out of here' - something to that effect, nobody's leaving - and pulls out a machete and unsheathes it and starts doing the unthinkable," he said.
Thomas was detained soon after and charged with attempted murder. He pleaded not guilty, and is being held in jail with his bail set at $5m (£3.8m).
State Governor Andrew Cuomo described the attack as "domestic terrorism", while President Donald Trump said the attack was "horrific".
"We must all come together to fight, confront and eradicate the evil scourge of anti-Semitism," the president said.
Are anti-Semitic attacks on the rise in the US?
On Friday, New York city police's hate crimes unit said it was investigating eight anti-Semitic incidents reported since 13 December.
They included a threat by a man who walked into an Orthodox Jewish community organisation's headquarters in Brooklyn and threatened to shoot someone. In another incident a 30-year-old woman reportedly slapped three women in the face.
New York Police Department commissioner Dermot Shea has said hate crimes in New York City are up 22% this year.
"You see a swastika being drawn, you see a brick being thrown through a window, you see a woman walking down the street with her kids and having her wig ripped off," he said.
In April a gunman killed a woman and wounded three people at a synagogue in San Diego.
That attack came exactly six months after the deadliest anti-Semitic attack in US history, when a gunman killed 11 worshippers at the Tree of Life synagogue in Pittsburgh.