Breaking his long public silence, Officer Darren Wilson on Tuesday said he shot and killed Michael Brown in Ferguson after a "fight for survival" and because he feared for his life.

A day after a St. Louis grand jury decided not to indict him, Wilson sat for a 45-minute interview with George Stephanopoulos that ABC News posted in full on its website Wednesday morning. Speaking calmly in a soft voice and showing no emotion throughout, Wilson repeatedly portrayed Brown as the aggressor during their altercation on August 9. The unarmed 18-year-old twice punched Wilson in the face as he sat in his police car, and the officer said in the interview that he took out his gun because he was afraid the physically larger Brown would beat him unconscious.

"The way I’ve described it is, it was like a 5-year-old trying to hold on to Hulk Hogan," Wilson said, repeating a description of Brown that he used in his testimony to the grand jury. "He was very large, [a] very powerful man." Evidence photos taken the same night showed Wilson only with redness on his cheek and no significant bruising, leading some to question his account of Brown's assault on him.

The first excerpts of the interview aired Tuesday evening as violence briefly broke out in Ferguson for a second straight night following the grand jury announcement. With a much larger National Guard presence, authorities said the evening was calmer than Monday night, with fewer arrests, while across the country large and mostly peaceful demonstrations took place in New York, Washington, Los Angeles, Oakland, and other cities. Marchers everywhere took over highways and roads, stopping traffic and snarling major arteries, but mostly avoided any violence or property damage.

Prosecutor Robert McCulloch has said that the grand jury brought no charges against Wilson because witnesses gave conflicting testimony about what they saw. While some had said Wilson shot Brown in the back or while his hands were up in surrender, other accounts matched the one Wilson gave to the grand jury and then to ABC News: that Brown assaulted the officer in his car and then, in a subsequent confrontation outside the vehicle, charged at him even after Wilson had fired several shots in his direction.

Wilson said he stopped Brown and another man he was with, Dorian Johnson, while they were walking in the middle of the road, after Brown had stolen a package of cigarillos from a nearby store minutes earlier. Initially unaware the two were suspects in a crime, Wilson said he asked Johnson to walk on the sidewalk when Brown responded aggressively and then slammed his car door shut as Wilson was trying to get out, pinning him inside.

When Brown began punching him, Wilson said he went through a mental checklist and concluded that taking out his gun was his only viable option. "The next thing was, how do I survive?" Wilson said he recalled thinking. "I didn’t know if I’d be able to withstand another hit like that."

He said his training "kicked in," and he realized he could not take out his mace or his baton to push Brown back. "The only option I had left at that point was my firearm," Wilson said. Still, the struggle continued. He said that at one point, Brown took hold of the weapon and Wilson thought he was going to "try and shoot me with my own gun." After he fired the initial shots, Brown ran away but then doubled back toward the car, Wilson said, even as he continued shooting. It was then that Wilson had told the grand jury he thought Brown looked like "a demon" based on the intensity of his expression.

Asked by Stephanopoulos about that characterization, Wilson didn't repeat it, but he said he still didn't know if Brown was armed and feared he might have a knife or a brick when he continued to charge back at him. "He will kill me if he gets to me," Wilson recalled thinking. When Brown got to within 8-10 feet of him, he said, he fired again and watched as the bullet went into Brown's head.

Stephanopoulos pressed Wilson politely, but not aggressively, throughout the interview. While Wilson said he was sorry that Brown's "life was lost," he showed no remorse about his actions and insisted he simply acted as he was trained to do. "I just did my job," he said. The killing and the grand jury decision has escalated racial tensions between communities of color and the police, but Wilson said neither racial animosity nor anger played any role in his actions toward Brown. "There was no time for anger. Training took over. It was survival mode," he said.

Wilson also revealed during the interview that he did indeed get married during the intervening weeks, and that his wife is now pregnant.

In a separate interview on CBS This Morning, Brown's parents, Leslie McSpadden and Michael Brown Sr., rejected Wilson's characterization of their son and his own actions. "I don't believe a word of it," McSpadden said. "I know my son far too well. ... He would never do anything like that. He would never provoke anyone to do anything to him and he wouldn’t do anything to anybody." On NBC's Today, Brown Sr. said Wilson's account "sounds crazy." "For one, my son, he respected law enforcement," he said. "Two, who in their right mind would rush or charge at a police officer that has his gun drawn?"