Apple CEO Tim Cook opened today’s Worldwide Developers Conference (WWDC) with a moment of silence for the victims of the weekend’s terrorist attack. Early Sunday morning Omar Mateen, a gunman who had reportedly sworn allegiance to ISIS, massacred 50 people and wounded at least 50 others at a gay nightclub in Orlando, Florida.

“We’d like to take a moment to talk about the tragedy that occurred yesterday in Orlando, Florida. We offer our deepest sympathies to everyone whose lives were touched by this violence. It was [a] senseless, unconscionable act of terrorism and hate aimed at dividing and destroying. The Apple community is made up of people from all around the world, from all different backgrounds, and all different points of view. We celebrate our diversity. We know that it makes us stronger and moves everyone forward.

“Please rise and join us for a moment of silence to honor the victims and the people who love them.”

Cook spoke to a packed Bill Graham Civic Auditorium in San Francisco and when he was done, he bowed his head and clasped his hands in front. After about 10 seconds, he said simply, “Thank you.”

Microsoft’s CEO Satya Nadella also voiced his concern this morning. On a press call with LinkedIn CEO Jeff Weiner discussing their planned $26.2 billion merger, he said: “Jeff and I wanted to take a moment to express our condolences and sympathies for the victims and the people or Orlando. There should be no place in the world for the violence and hatred exhibited this weekend.”

Cook’s statement today highlighted that the mass killing in Orlando is a grave threat to America and worrisome for singling out gay people. ISIS online propaganda includes videos of gay men being pushed from tall buildings and being stoned to death. It’s possible that Mateen may have been influenced by ISIS, or by the views of his father, who reportedly holds anti-gay views.

Cook, who in 2014 declared, “I’m proud to be gay,” has been a quiet but strong leader on many social issues from labor rights to same sex marriage to the environment. Last spring, Cook had attacked a wave of anti-gay legislation in an op-ed for the Washington Post. He argued that such laws are both bad for business and a step backward morally. “These bills rationalize injustice by pretending to defend something many of us hold dear,” Cook wrote. “They go against the very principles our nation was founded on, and they have the potential to undo decades of progress toward greater equality.”

While Cook’s comments were brief, they were consistent with his approach of walking softly and carrying a big stick.

Additional reporting by Chris O’Brien.