Just last week my older son did the same thing to us but from our home. We know he can undo locks and open doors so we installed a chain lock at the top of the door so that he can't reach it because he is always trying to get outside. We rarely use the front door, we go in and out of the garage which is blocked off by a baby gate.
Not 10 minutes before his escape I had walked by and saw him playing by the window and glanced at the door to make sure the chain was locked like I always do and it was, I went to the couch in the other room to change my younger son (3 months) and right around the time I was done my husband walked downstairs with a basket of laundry and I noticed that I didn't hear our son say anything, usually we at least get a "hi" or "mama" or "daddy" when one of us walks by so I asked my husband if our son was still playing in the front room and he said he thought so but I saw the realization dawn on him that he didn't remember seeing him so we both rushed to the front door, saw that it was cracked and that the chain was undone we both frantically ran out the front door just in time to see a man walking down our street carrying our son looking for his family, he had taken off his own coat to bundle up our son. It was maybe 30 degrees outside, he was only wearing his pjs, no shoes, and our son was so happy to be outside exploring and so oblivious to the cold and all the possible dangers, he saw a cat and just followed it down the street trying to catch it. It terrifies me that had he darted out into the street in front of w car or had the wrong kind of person seen him and taken him that those few minutes could have changed our lives forever.
Maybe that's why this case is getting to me so much, aside from the close age and physical similarities between my son and Noah, just last week under different circumstances this could have been us on the news with the child who just vanished. And so many people are so quick to judge and tear apart the grandmother for taking her eyes off of him for a minute and to bash the parents for having her babysit, it just irks me so much. Nobody realizes that things like this can happen in the blink of an eye even to the most attentive, protective, helicopter parents.
We still don't know how the chain came loose, my best guess is that whenever it was locked last maybe the slide was only put halfway into the track by mistake so when he tried the door it just fell out.