A soldier who died in an explosion of a Tesla Cybertruck at the Trump hotel in Las Vegas left a note saying it was a stunt to serve as a "wakeup call" for the nation's ills, investigators say.
Matthew Livelsberger, a 37-year-old Green Beret from Colorado Springs, Colorado, also wrote in the note that he needed to "cleanse my mind" of the lives lost of people he knew and "the burden of the lives I took".
Mr Livelsberger apparently harboured no ill will towards US President-elect Donald Trump, Clark County sheriff's officials said.
"Although this incident is more public and more sensational than usual, it ultimately appears to be a tragic case of suicide involving a heavily decorated combat veteran who was struggling with PTSD and other issues," FBI special agent in charge Spencer Evans said at a news conference.
The explosion caused minor injuries to seven people but virtually no damage to the hotel.
"This was not a terrorist attack, it was a wakeup call. Americans only pay attention to spectacles and violence. What better way to get my point across than a stunt with fireworks and explosives," Mr Livelsberger wrote in a letter found by authorities who released only excerpts.
Investigators identified the Tesla driver - who was burned beyond recognition - as Livelsberger by a tattoo and by comparing DNA from relatives.
The cause of death was a self-inflicted gunshot to the head, according to coroners' officials.
Pentagon officials have declined to say whether Livelsberger may have been suffering from mental health issues but say they have turned over his medical records to police.
The new details came as investigators sought to determine Livelsberger's motive, including whether he sought to make a political point with the Tesla and the hotel bearing the president-elect's name.
Tesla chief executive Elon Musk has recently become a member of Trump's inner circle.
Neither Trump nor Musk was in Las Vegas early on Wednesday, the day of the explosion.
Both had attended Trump's New Year's Eve party at his south Florida estate.
Musk spent an estimated $US250 million ($A402 million) during the presidential campaign to support Trump, who has named Musk, the world's richest man, to co-lead a new effort to find ways to cut the government's size and spending.
Investigators suspect Livelsberger may have been planning a more damaging attack but the steel-sided vehicle absorbed much of the force from the crudely built explosive.
