Image copyright Stranger Fruit Image caption The video is unclear, but a filmmaker believes Brown's death was due to a marijuana deal gone wrong

A newly disclosed surveillance video from the hours before the killing of a black man in Ferguson, Missouri, in 2014 has triggered fresh protests.

A filmmaker has released the footage which he says shows Michael Brown did not rob a shop, as police claimed, but instead exchanged marijuana for cigars.

He says it contradicts video released by police showing Brown threatening the shopkeeper as he walks out with cigars.

The 18-year-old was shot dead by a police officer moments later.

However, the convenience store maintains it was a robbery.

Policeman Darren Wilson was cleared of wrongdoing by investigators but the teenager's death led to violent protests and a national debate about lethal police force against African Americans.

On Sunday night, 100 people gathered outside the shop after news emerged of the new video.

On Monday, one St Louis man was charged with trying to set fire to a police car.

Henry Stokes, 44, was arrested by police after he was seen placing a napkin in the gas tank of a police car and trying to use a cigarette lighter to set fire to it.

Image copyright Getty Images Image caption Police cleared the car park of protesters on Sunday night

Image copyright Reuters Image caption Armed police arrived after the crowd grew to nearly 100 people

The previously unreported footage shows Brown entering the Ferguson Market and Liquor around 01:00 on the day of his death.

He approaches the counter and hands over an item that appears to be a brown bag, and in exchange takes a shopping bag filled with cigars.

After walking towards the door, he then turns around and returns the cigars to the counter before leaving.

Jason Pollock, the filmmaker releasing the tape as part of his documentary Stranger Fruit, says it proves that Brown had not been committing a robbery when he returned to that store around noon later in the day.

In that encounter, he is seen shoving store owner Andy Patel before leaving with the cigars.

St Louis County prosecuting attorney Robert McCulloch said investigators had been aware of the video all along and determined it was not "admissible".

"It was determined that it was neither relevant nor material to anything that happened that day," he told reporters in a news conference.

He added: "This is not new information. It's certainly not a surprise to anyone."

Media playback is unsupported on your device Media caption CCTV pictures show a alleged robbery that took place minutes before Michael Brown was shot

Video of Brown appearing to rob the shop was released by police to support their claim that he was stopped by police because he was a suspect.

Mr Pollock's film claims that the marijuana was exchanged as part of a pre-negotiated deal, and that Brown had then decided to leave the cigars behind the shop counter for safekeeping.

"They destroyed Michael's character with the tape, and they didn't show us what actually happened," Mr Pollock told the New York Times.

"There was some type of exchange, for one thing, for another," says Lesley McSpadden, Brown's mother, in the new film, which is debuting at the South by Southwest festival in Austin.

Image copyright AFP Image caption A temporary memorial marks the location where Brown was shot (file image)

Jay Kanzler, a lawyer for the convenience shop, said they would release more footage to prove it was a robbery.

"There was no understanding. No agreement. Those folks didn't sell him cigarillos for pot. The reason he gave it back is he was walking out the door with unpaid merchandise and they wanted it back."