Dallas, Texas: On the morning after, the nation is roiling but downtown Dallas is eerily quiet, save for the emergency response convoys and dozens of cops securing the scene of the brutal and bloody murder of five of their colleagues by sniper fire on Thursday evening – and another noisy Black Lives Matter protest march.

Despite earlier suggestions of a complex strategy that involved several gunmen, by midday Friday investigators were leaning towards a belief that the whole operation had been the work of a single gunman – identified as Micah Johnson, a 25-year-old US Army reservist veteran.

An engineer who specialised in carpentry and masonry, Johnson had served in Afghanistan as recently as July 2014. His Facebook page, now removed, has pictures of him wearing an African dashiki shirt and raising his fist in a black power salute; and others of him in military uniform.

Local media reports say investigators were sweeping what was described as the Johnson family's imposing home, in well-heeled Mesquite, in the greater Dallas area. The same reports say Johnson was not a known criminal and was not believed to have ties to foreign terrorist groups or to American activist movements, like Black Lives Matter or the New Black Panthers.

But he was part of an informal gun club that "took copious amounts of target practice," the reports say.

Neighbour Jowanda Alexander told The Guardian she had met Johnson once, five or six months ago, when he had dropped by her home to complain about her daughter "messing with his mailbox".

"When he came he didn't come aggressive, just real gentle and he seemed real nervous," she said. "[But] It's scary because you just never know who your neighbours are."

An horrific drama, it all climaxed when police dispatched a robot carrying a bomb into a parking garage at El Centro College, on Main Street, where Johnson was holed up on the second floor. When attempts to negotiate his surrender failed, there was a 45-minute shootout before the bomb was detonated remotely – killing the suspected sniper.

"Negotiations broke down, and we had an exchange of gunfire,," Dallas Police Chief David Brown told a Friday press conference. "We saw no other option but to use our bomb robot and place a device on its extension, [and] for it to detonate where the suspect was."

The police have released little precise information on an evening of urban butchery that unfolded before media cameras and a battery of  mobile phones, which produced video that went viral. But we have yet to get a precise narrative that explains how a peaceful protest by thousands, including many family groups, over African Americans as victims of questionable police killings, became a crazed massacre of cops doing their job.

An exception is a riveting eyewitness account by Ismael Dejesus, who was a guest in the Crown Plaza Hotel. From his hotel room, he video-recorded some of the action and told CNN of a cold-blooded and methodical killer's casual approach to life and death in the streets of Dallas.

Talking over his video, Dejesus recounts observing a shooter dressed in tactical clothing alight from a Chevy Tahoe S.U.V. He explained: "Man had a rifle, AR-15, clear as day; pretty big magazine. And you can see towards the end of the video here that he goes ahead and drops a few mags.

"He had multiple pockets, he had three to four pockets in front of his pants. He definitely looked like he was wearing something in his shirt. He got out of there, walked over to the pillar, put a magazine in and started firing.

"It looked like an execution honestly. He stood over (the officer) after he was already down and shot him maybe three to four times in the back. It was very disturbing to watch."

Authorities are tight lipped about three others suspects, one a woman taken from El Centro garage, who are in custody – except to say they refuse to divulge information on any role they might have had in planning, providing for and executing an attack which, as a response to events as recent as 24 hours previous, had to be planned in a hurry.

An unnamed, Dallas Police Department commander was quoted, described the shooting as a "conspiracy" that involved several people in the planning, logistics and execution of a coordinated attack.

Disturbing claims to the police, by the gunman that a series of bombs had been planted around the city and "that the end is coming and he's going to hurt and kill more of us — meaning law enforcement," proved to be unfounded.

A precise motive remains clouded.

Sharing scant detail on an hours-long standoff with Johnson, Police Chief Brown said that the gunman told police negotiators "he was upset about Black Lives Matter; " "he was upset about the recent police shootings;" and that "he wanted to kill white people, especially white officers."

"The suspect said that he was not affiliated with any groups and he stated that he did this alone. The suspect said other things that are part of this investigation," Brown said, adding that the protest rally and march had been peaceful.

Missing in that mix was any clear sense of why Johnson was upset about Black Lives Matter, an influential new activist group that has emerged in 2013 response to a slew of blacks being killed by cops.

And in the absence of any claimed or apparent link to international terrorism – the so-called Islamic State and other such movements – this one is on America, a country that defends the right to bear high calibre weapons with a single-minded ferociousness that leaves much of the rest of the world agape. And there was no expectation Friday, that new calls for meaningful gun control would be any more successful than those that regularly follow America's serial massacres.

In the immediate aftermath of massacre, the police chief Brown said that two snipers were involved. But at a press conference early on Friday, he referred to just a single shooter – raising questions about the level of expertise and the sophistication of the weaponry needed to pick off targets among a force of about 100 cops in a protest crowd estimated at 800 – as the evening light faded.

But the city's former deputy police chief, Craig Miller, told reporters: "If what we believe actually took place, where officers were shot in the back in some instances from elevated, perched positions, and perhaps the bad guy was using armor-piercing bullets — that'll change the dynamics in the body armour that the police officers use, how that body armour is worn [and] whether or not body armour is worn."

Brown explained more investigative work was required before he could comment on the possibility of a link between the gunman and the demonstration. But observing that the killer or killers obviously had knowledge of the protest route, he asked: "How would you know to post up there?

"So we're leaving every motive on the table of how this happened and why this happened. We have yet to determine whether or not there was some complicity with the planning of this, but we will be pursuing that."

Appealing to the public to support his force, Police Chief Brown said: "We don't feel much support most days – let's not make today most days.

"We're hurting, our profession is hurting. There are no words to describe the atrocity that occurred to our city. All I know is that this must stop, this divisiveness between our police and our citizens."

The Police Department was holding back information on the dead policemen, but the heart-breaking story of Officer Patrick Zamarripa emerged as members of his family shared their grief as impromptu memorials of flowers, stuffed toys and candles appeared around the city.

Watching news reports of the drama, his grandmothers reportedly became distressed -"Gimme the phone – I got to call Patricio," according to the Dallas Morning News.

About the same time, Zamarripa's partner Kristy Villasenor was out with their 2-year-old daughter. She snapped a selfie of the two of them and posted it to Facebook – tagged for the father to see.

Relieved, a friend of the family read the photo to mean that the father, mother and daughter were at the ball game together, and wrote her own Facebook post – "Glad Pat is there and not in Dallas right now..."

But Zamarripa was downtown – and he was dead.