oath keepers
Members of the Oath Keepers walk with their personal weapons on the street during protests in FergusonReuters

As hundreds gathered in the town of Ferguson to commemorate the one-year anniversary of the shooting of 18-year-old Mike Brown, it was the appearance of just a few that caused many to be alarmed.

Heavily armed, wearing military-style bullet-proof vests and assuring residents they have "got their backs", four men seen among the protesters identified themselves as members of the Oath Keepers – a group who described themselves as current and former serving military and police, who "pledge to fulfil the oath all military and police take to defend the Constitution against all enemies, foreign and domestic".

The white men seen "patrolling" the predominately black area of the Missouri town with assault rifles during the anniversary of an already racially charged event were described as "both unnecessary and inflammatory" by St Louis County Police. The group were also described as a "fiercely anti-government, militaristic group" by civil rights organisation the Southern Poverty Law Center.

oath keepers
Police in riot gear clashed with protesters who had gathered in the streets of FergusonReuters

But rather than inflame tensions during the demonstrations, members of the Oath Keepers claim they were at the Ferguson protest to protect journalists working for InfoWars, the infamous conspiracy website run by US radio host Alex Jones.

The Oath Keepers previously took it upon themselves to guard Ferguson homes and businesses during riots in November 2014 following a grand jury's decision not to indict officer Darren Wilson for shooting Brown by standing on rooftops with their guns. The group was ordered to leave by police over fears it could incite more fear in an already tense situation.

"We were sick in our gut we couldn't be here sooner," John Karriman, a state leader of Oath Keepers who teaches police tactics, told the St Louis Post Dispatch. "We are here to volunteer our time and make sure everybody stays safe."

Founded in 2008 by Stewart Rhodes, an ex-paratrooper, the Oath Keepers are believed to have more than 35,000 members across the US who all go by the group's motto: "Not on our watch!"

However, many have accused the group of vigilantism due to its militant approach to its ideas, which include not obeying "unconstitutional orders, such as orders to disarm the American people".

In a profile on the group by Mother Jones, the website describes the Oath Keepers as "unique" because its "core membership consists of men and women in uniform, including soldiers, police, and veterans".

It adds: "At regular ceremonies in every state, members reaffirm their official oaths of service, pledging to protect the Constitution — but then they go a step further, vowing to disobey 'unconstitutional' orders from what they view as an increasingly tyrannical government."

A few weeks after the Ferguson protests first began in August 2014, footage emerged of a former police officer giving a speech to the Oath Keeper's St Louis chapter in which he can be heard saying: "I'm also a killer. I've killed a lot, and if I need to I'll kill a whole bunch more. If you don't want to get killed, don't show up in front of me. I'm into diversity – I kill everybody."

The group was forced to issue a statement assuring officer Dan Page of the St Louis County Police Department was not an official member of the Oath Keepers and he does not "reflect the opinions of our local Oath Keeper Chapter, nor the national organisation".

A statement on the group's website reads: "Oath Keepers reaches out to both current serving and veterans to remind them of their oaths, to teach them more about the Constitution they swore to defend, and to inspire them to defend it."