The San Diego synagogue shooting suspect allegedly wrote a manifesto claiming to draw inspiration from the New Zealand terror attack.
John T. Earnest, 19, was arrested after the shooting on Saturday morning that left one woman dead and several other injured.
The 19-year-old is alleged to have fled the scene of the shooting, on the last day of Passover, before surrendering to police a short while later.
He is said to be the apparent author of an unconfirmed manifesto in which he claimed responsibility for an unsolved arson attack on a nearby mosque last month.
The teenager, believed to be a California State University nursing student, also said he drew inspiration from the gunman who killed 50 people at two mosques in Christchurch.
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Police say they are now investigating claims Earnest was involved in the attack on the Islamic Center of Escondido in which no one was hurt.
San Diego County Sheriff Bill Gore said the suspect had "no prior criminal record".
He added: "We have copies of his social media posts and his open letter and we'll be reviewing those to determine the legitimacy of it and how it plays in to the investigation,"
The horrific attack took place six months after a gunman stormed the Tree of Life synagogue in Pittsburgh yelling, "All Jews must die."
The assailant in that massacre, said to be the deadliest attack ever against Jews on US soil, was arrested.
Poway Mayor Steve Vaus said Saturday's shooting was a "hate crime".
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A rambling, violently anti-Semitic, anti-Muslim screed written by an individual calling himself John Earnest was found posted online before the attack.
In the 4-000 word letter the author claims credit for the Escondido mosque arson, which was put out by congregants.
The author is reported to have written: ''If you told me even 6 months ago that I would do this I would have been surprised."
Before adding: "Tarrant was a catalyst for me personally."
Speaking with reporters at the White House, U.S. President Donald Trump said, "My deepest sympathies go to the people that were affected."
He added that "it looks like a hate crime" and that authorities will "get to the bottom of it."
Four people were struck by gunfire in the attack with an "older woman" dying, and three others in a stable condition.
One of the victims is a rabbi, Yisorel Goldstein, who underwent defensive wounds to his fingers.
As the suspect was making his getaway, an off-duty U.S. Border Patrol agent opened fire striking the vehicle.
The gunman was arrested a short time later when he gave himself up to police.
An assault-style rifle believed to be the murder weapon was found on the front passenger seat of the car.
