I have a Belgian Malinois/GSD X who is fine outside the yard and I take him everywhere with me, but his yard is a whole different level. We have an invisible fence (hate it) and some of my neighbors don't confine their dogs that well. We've had several close incidents before. He had severe aggression issues when I first got him, he flunked out of Police Dog training and was to be put down, but I decided to give him a second chance at life. Now as I said earlier, after a year of training, I take him everywhere with me. He's fine with other animals and children now. However, he does not like boston terriers that wear shirts. XD
Everyone already mentioned everything I could think of. Sympathy card or flowers, a memorial, or a letter of apology.