Dallas - When officers who'd been shot by a sniper in downtown Dallas started showing up at Parkland Memorial Hospital, trauma surgeon Dr Brian H Williams went to work, pushing aside the inner conflict he faces every day as a black man who's fearful when encountering police.He sees the news about black men dying at the hands of police. He sees the aftermath of those killings and recoils when the victim is demonised or defamed. He's had his own encounters with police in which he thought he might die. But he also knows the sacrifices that police officers make putting their own lives on the line each day.His voice quivering as he expressed regret on Monday at the officers' deaths at the storied hospital, Williams also gave voice to the intense racial turmoil roiling the country."All I wanted to do was save those police officers. And we did everything but we couldn't do it," he said with a deep sigh. "I admit I have my own burdens that I carry when I deal with law enforcement, but that was not an issue for me at that time. These were my patients."It was near the end of what had been a peaceful protest against recent fatal police shootings that a 25-year-old man wielding a semi-automatic rifle fired on officers who were patrolling the demonstration. The first call came about an officer being shot; moments later, there were a flurry of notifications that even more victims were on the way.It quickly became evident that something catastrophic had happened. Five officers were killed, nine others were injured as well as two civilians: the deadliest attack on police since 9/11.The hospital's hallways were abuzz with activity, the usual rings and beeps of machinery, the doctors and nurses moving in and out of treatment rooms, police lined up in the hallways praying for their wounded colleagues.Williams reckons he walked back and forth in front of the crowd of officers dozens of times."I certainly during that time felt the despair they were going through. I knew that they were angry at this assailant. ... It was palpable and I felt it," Williams told the AP. "But I also had a personal understanding of where that [anger against police] all came from. Not that I condone what happened. I certainly abhor the results. But I can see where the roots of that have been laid. "The gunman, Micah Johnson, was a black Army veteran who followed black militant groups online. His parents said his military service changed him and he became a hermit.ThreateningA self-described military brat who moved around a lot as a child, Williams turned to medicine after spending six years in the Air Force as an aeronautical engineer. He got his medical degree from the University of South Florida in 2001, did his residency at Harvard's Brigham and Women's Hospital in Boston, and a fellowship at Emory University's Grady Memorial Hospital in Atlanta before joining Parkland - the same hospital where President John F Kennedy was brought after he was shot - six years ago. He's married with a 5-year-old daughter.He's been stopped by police himself over the years and said he is mindful each time that he must act and speak in a way that doesn't seem threatening. He lives each time in fear that he could be killed. He sees the news about other black men killed by police.In one traffic stop, he ended up "spread eagle" on the hood of the cruiser. In another, when he was stopped for speeding, he had to wait until a second officer arrived. Just a few years ago, he was stopped by an officer and questioned as he stood outside his apartment complex waiting for someone to pick him up and drive him to the airport.He doesn't have such encounters every day but when he does, he's on his guard and, "I'm always just praying for the encounter to end."As Friday morning turning into Friday night, the trauma unit's efforts came to an end. They had done all they could and it was time to bring the bodies of those they were unable to save to the medical examiner.Police were lined up in the ambulance bay, the blue line in full force to escort and pay respects to their fallen colleagues. Williams joined the officers, standing with them in their formation."I didn't know if I belonged with them. I was a civilian. I don't go through the daily challenges that they go through. I don't put my life on the line every day like they did," Williams said, tearing up. "But I was grieving with them. I felt the same degree of sorrow. And I wanted to show my respects. ... I hope that what I did was not offensive to them. But I wanted to show my appreciation to them."Through it all, Williams can't help but question why he was there that night. He wasn't supposed to be, except for a last-minute schedule change."I wonder if this was the reason that in the midst of all this racial tension and dead black men and violence against cops - was I the one put there to experience this and tell my story and get the conversation started?" he said.