..from the autopsy of Ninoy Aquino, it was found out that the bullet enters from the back of his head and exit near his chin. He was walking down the staircase, the angle of the bullet is downward, or specifically slanted, obviously because the Gunman was walking behind him.
Galman was not from the inside of the Plane, he was from somewhere else outside, he was positioned below the place where Ninoy was walking. It is possible that Galman was put there as a decoy, they will shoot him after Ninoy was assasinated to make it look like that it was him who shoot Ninoy. It is impossible that Galman just infiltrate the airport, with 1000+ security around it, he won’t stand a chance, unless someone put him there, or someone that has control over those security let him pass. Now the question is, why do they need decoy? Are they protecting the real gunman? It is known that personal securities were sent to escort Ninoy that day. It is possible that it is one of them.
One mystery is that not many saw how he was shot. So possibly the gunman positioned the gun which it isn’t obvious for everyone. He might have something to conceal the gun from the sight of those around him. The plane is crowded, it would be easy if he is using a handgun.
There are still many questions, it is also possible that not all the guards who escorted him knew about the assassination plot.