How did the T-Rex kill everyone on the boat?

I think this is a plot hole of the movie. We really don't know what happened aboard the ship, except that the T-Rex was tranqualized and then counteracted.

There were 2 T-Rexes, but as told to Ian Malcolm (Jeff Goldblum), the infant T-Rex was brought back on the plane. This person was obviously there for the loading of the T-Rex on the boat, witness to the injections, who then accompanied the baby on the plane. Only the adult T-Rex was on the ship, tried to escape through the cargo hold doors (they were ajar, maybe warped from the inside), then escaped when the doors were lifted by the guard after arrival.

All this would suggest that some human being locked the T-Rex in the cargo hold AFTER the slaughter, but who could do that, and with what bait? AND, if there was someone still alive, why drive the ship into the dock at full speed?