Believe it or not, the shooting ambush of the Dallas police officers on July 7 in all likelihood was not too difficult to pull off. It was a planned attack, but it did not require complex skills. The New York Times has a good article on how the events unfolded.
1. Learn the route of the march.
2. Pick your ambush site.
3. Recon your ambush area and where you are attacking from.
4. Assemble weapons and gear.
5. Infiltrate target and hide until go-time.
Learning about the route of the march wouldn't be difficult. It would probably be on social media and a little social engineering to get the info direct from an organizer is not hard to do.
(Details on the actual shooting are sketchy at the time of writing, so part of this is supposition)
Once you know where the march is going, you can pick your sniper's nest. A high location over looking a city street is a perfect location for a sniper. Lee Harvey Oswald picked the 6th floor of the Texas School Book Depository overlooking Dealy Plaza just blocks away when President Kennedy was shot.
The sniper may have shot from a 10-15 story parking garage at the corner of S. Lamar and Main St. (borders Commerce St. and S. Austin St.). A high perch on an urban street provides a field of fire that is relatively unobstructed and where good cover for the 'targets' is lacking. There was also no need to target a specific person; just anyone in a uniform was a target, negating the needs the assassin-sniper of movies to wait and fervently look for a needle in a haystack. It was like shooting fish in a barrel.
A parking garage is fairly empty. People don't hang out in parking garages; they park their car and leave, only to return after their business elsewhere and immediately drive out. There is seldom anything worth spending time in a parking garage for, meaning that depending on the traffic level and the exact location of the shooter, it's not all that difficult to hide, especially in a car, until it's time to shoot.
The shooting wasn't all that complicated either. The shooter was firing at a distance of probably 100 to 300 feet maximum; an easy shot for a trained shooter, military or not, with iron sights. With a decent scope, that distance easily doubles. With the targets below the sniper, horizontal cover is negated until they get behind something tall enough to block the line of sight. The targets can run, but they can't hide so easily as if the shooter was at street level. A good marksman can follow the moving targets and hit them.
Also, a well concealed sniper can shoot at suspect who have taken cover, mistakenly believing they are safe. The shooter may have benefit from the panic of police not knowing where the shots were coming from and shooting at officers hunkering down wherever they were, not knowing they were within the line of fire. Imagine the terror of thinking you are safe behind your car all the while you are totally exposed to the nutjob with a rifle.
Complexity does come in when it comes to an escape or multiple attackers. Multiple shooters would likely have to coordinate fields of fire, dividing up the areas where each will shoot and not shoot. if there were shooters also on the ground, fields of fire and planning on what each person is going to do is more important to avoid accidentally engaging each other. Escape plans and routes are the main concern. Where to park the getaway car(s)? What route to use and what are the alternates? What are the plans if police try to stop you? What the plans for a counter-sniper or counter-assault?
Powerful rifle? No. An AR-15, especially if using military surplus
ammo, will easily defeat soft body armor worn by police. Funnily enough,
if this guy had been using a scoped deer rifle like Charles Whitman,
that rifle would have been a more powerful combination, potentially
capable of defeating even hard armor and punching through vehicles. Update: It may have been an SKS rifle, which is not magazine fed unless modified and the round is slightly more powerful than a AR-15 5.56mm round, but not as powerful as a full-size rifle cartridge.
Planning and carrying out this kind of attack seems complex because to the average person, they don't think about these things. They are not police, who have to plan to counter sniper ambushes, the military, who does this for a living, or a psychopath. Someone with basic military training, heck, even someone who reads and studies military tactics, or even plays realistic first-person shooter video games can gain enough knowledge to successful pull something like this off.
This attack was a depraved perversion of justice. It was calculated and deliberate in its aim to take revenge against police for perceived injustices. It did take some planning, yet it was not a highly orchestrated attack that required experts. No, all it involved was one or more persons who know how to shoot and who had considered all I that I have written above. God help us if we begin to see worse attack like this, such as the truly coordinated, multiple location ISIS attacks in Paris of last year. As shocking as this was, we ain't seen nothing yet.