Update: Dallas Police have cleared Mark Hughes as a suspect and released him from custody.

Original article: A rifle-toting man whose photo was posted by Dallas police as a person of interest after four police officers were fatally shot during a Black Lives Matter protest is innocent, said his brother.

The man in the photo was circulated by police who appealed to the public for help locating him. He has been identified as Mark Hughes, who attended the protest wearing a camouflage T-shirt and toting a long rifle, possibly an AR-15 assault rifle, which is reportedly legal to carry in Texas.

Hughes surrendered to police and handed over the gun he had slung on his back, said officials.

Corey Hughes, a protest organizer who claimed to be the brother of the person if interest, told CBS News affiliate KTVT that he is "100% sure" Mark Hughes was not a gunman in the attack on police in downtown Dallas.

Hughes said his brother brought the weapon to the protest — which he said was unloaded — simply to exercise his Second Amendment rights to bear arms.

"My brother was marching with us. Because he's my brother and I understood the severity of the situation, I told my brother, 'Give that gun away,'" Hughes said. He insisted that he witnessed his brother hand his weapon over the police.

"He never thought that by exercising his right he's be plastered over the national media as a suspect," Hughes said. Corey said his brother handed over his firearm to a police officer as soon as shots were fired in the downtown attack.

Several twitter friends of Mark Hughes pleaded with Dallas police to take down Hughes' photo, but his image remained on the police department's twitter site.

At the time of reporting, four police officers have been shot dead and 11 have been injured by two snipers on Thursday evening (7 July) during a Black Lives Matter rally held in Dallas. Witness said they heard dozens of gunshots in the downtown area of the city around 9pm local time (3am BST).

Three suspects - two men and a woman - have been arrested. One gunman remains at large at a garage at El Centro college. Dallas Police Chief David Brown said the suspect claims there are bombs "all over" the city.

The Dallas Police Department said in a statement before midnight that a female suspect who was in a shootout with Dallas SWAT officers near the garage at El Centro College downtown was in custody.

Brown said later that police were negotiating with a second suspect on the second floor of that same parking garage. He said the suspect had exchanged gunfire with police during the negotiations, which were ongoing. Brown said the suspect told negotiators "the end was coming," that he's "going to hurt and kill more of us."