a.i) Earlier when Spurius Brontosaurus sees Asterix and Obelix overcome some bandits, he began his plan to steal the magic potion that increases Asterix's strength.
His plan is to overcome both of the Gauls and take the boy Pepe back.
Spurius gets out of bed to steal the magic potion of strength once Asterix has gone to sleep
a.ii) Burke unleashes the live facehuggers from their containers in the room where Newt and Ripley are sleeping to impregnate them
b) Burke and Spurius Brontosaurus are caught red handed
b.i) Spurius Brontosaurus is caught stealing the potion
Asterix possibly awakened by Obelix talking loudly to the dog in the next room, wakes up to find Spurius Brontosaurus stealing the potion
He yells out pointing at Spurius with his finger "What are you doing with the magic potion, Stop thief!", but Spurious runs off through the door
It appears hat Asterix never trusted Spurius anyway
b.ii) Carter Burke is caught trying to infect Ripley and Newt with face huggers
It appears that Carter Burke has unleashed the face huggers onto Ripley and Newt when they are sleeping, and ignores their cries for help as they are trapped with the creatures.
The marines come to rescue Ripley and Newt.
Ripley accuses Burke and so the Colonial Marines have turned on him as well
Having accused Burke earlier on with killing the colonists by sending them out to the derelict, now she has reason to accuse Burke of trying to have the Facehuggers implant her and Newt with alien embryos to try to get them back through quarantine
Brontosaurus escapes through a doorway and down an outside passage, but bumps into a Roman soldier and ges arrested.
c.ii) Burke escapes through the corridor but meets his doom
As the aliens launch an attack through the ceiling and floor,
Burke escapes through a corridor, but gets caught by the alien beasts.
Perhaps as shown in a scene cut from the film, Burke is cocooned in the alien hive