Ryan Wesley Routh lay in wait for Donald Trump for almost 12 hours before he was spotted by Secret Service agents, according to court documents.

The alleged would-be assassin fled the scene before he was arrested 45 minutes later, with dramatic bodycam footage showing the moment heavily armed Sheriff’s officers and police dogs surrounded the 58-year-old suspect.

“Driver, take two steps to your right. Driver, go straight back. Keep walking,” a law enforcement official can be heard screaming before Routh steps into the frame and is apprehended.

Martin County Sheriff’s Office released the footage as a “smiling”, “calm”, and “polite” Mr Routh appeared in court for the first time.

Despite the dramatic arrest, Martin County Sheriff William Snyder said Mr Routh was calm “as if he was going for dinner”.

“His facial affect was so flat. His demeanour was relaxed,” he told CNN.

FBI Special Agent Mark Thomas wrote in an affidavit that when Mr Routh was asked if he knew why he was being stopped, “he responded in the affirmative”

In the affidavit, the FBI alleged that Mr Routh’s mobile phone was located on the edge of the Trump International West Palm Beach golf course as early as 1.59am on Sunday, local time.

A gun barrel was seen in that spot almost 12 hours later at 1.30pm, when Mr Trump was just 275 to 457 meters away on the fifth hole.

Acting Secret Service director Ron Rowe revealed Mr Routh “did not fire or get off any shots” before an agent opened fire as soon as he spotted the suspect’s rifle.

Sherrif Ric Bradshaw said the suspect did not seem to have a clear shot at Mr Trump before he was confronted.

“From where [the gunman] was at, he would have had to wait for the president to get up to that hole and then turn and face going toward the area he was at,” Mr Bradshaw told “Fox & Friends.”

“It doesn’t appear to me, knowing what I know about the terrain there and where we are looking at, that he had a clear shot from there to where the president was before he would make the turn to come that way [down the sixth hole].”

The loaded SKS-style semiautomatic assault rifle with a scope, which had its serial number scratched off, was found in the alleged sniper’s nest along with a digital camera and two backpacks, according to the criminal complaint. Authorities suspect the weapon “previously travelled in interstate or foreign commerce”.

Mr Routh was charged with initially possessing a gun with a scratched-out serial number and possessing a gun illegally as a felon. More serious charges are expected.

Reporters in the court described Mr Routh as wearing a blue inmate uniform and cuffs on his wrists and ankles, adding that he spoke “calmly and politely” as he appeared before Judge Ryon M McCabe.

He told the court that he makes about $A4,450 a month but has “zero funds” in savings and “zero” real estate assets. He owns two trucks in Hawaii worth “probably $1,000 ($A1,500) each”, and has one dependent, a 25-year-old son.

Photos taken outside a home in Hawaii, which was said to be where Mr Routh lived, showed a truck with a “Biden-Harris” bumper sticker.

Authorities raided a North Carolina also said to be used by Mr Routh, with an officer wearing a bulletproof fest yelling “police, make yourself seen”, according to video published by the UK’s Times.

Speculation over Mr Routh’s political links intensified after social media posts appeared to show an anti-Trump, pro-Ukraine ideology.

Ukraine denied links to Mr Routh as President Volodymyr Zelenskyy denounced political violence and sent his “best wishes” to Mr Trump.

In a self-published book last year, Mr Routh had blamed himself for voting for Mr Trump in 2016, saying he “misjudged and made a terrible mistake.”

Iran I apologise,” he added. “You are free to assassinate Trump as well as me for that error in judgment … No one here in the US seems to have the balls to put natural selection to work or even unnatural selection.”

Mr Routh, who has a previous conviction from the early 2000s after barricading himself inside a building, did not enter a plea to the charges. A bond hearing was set for September 23, local time, with an arraignment on September 30 to enter a plea.

He reportedly “laughed and smiled” while speaking to his legal team, but frowned when prosecutors asked he be held in custody until his next court appearance.