If Nebula had been the only one in his theory, Supergiant would not have needed to be careful at all, but everyone could feel just how much Thanos doted on Gamora.
Even though Gamora had already betrayed Thanos, Supergiant was not naive enough to think that his own weight in Thanos's heart could compare to even half of Gamora's...
That was why, when it came to matters involving Gamora, Supergiant had no choice but to be even more cautious. After all, his position within Thanos's team was rather awkward now. Once Thanos gained control of the Mind Stone, Supergiant's abilities had begun to seem somewhat redundant.
"It's not impossible that Nebula or Gamora made a move. Do you have no information at all about the person who killed your brother? What weapon was your brother killed with?" After hearing Supergiant's words, Thanos fell silent for a while. Then the Mind Stone on the Infinity Gauntlet released a glow, and the purple-skinned alien instantly felt his mind go hazy. Immediately afterward, an image appeared inside the spaceship.
It was the scene from the purple-skinned alien's memory of his brother and the corpses of acquaintances strewn across the ground. Thanos's gaze focused on the wounds of the dead, and he instantly recognized what weapon had caused them...
Because that was the weapon Thanos had given Gamora!
When he recognized what weapon had caused the wounds, to be honest, Thanos felt very conflicted. He was saddened that his most beloved daughter, Gamora, had ultimately still walked the path of betraying him, yet at the same time, he was somewhat gratified by Gamora's decisiveness in killing and the tightness of her lips.
In order to keep the information about the Soul Stone from being exposed, Gamora had not hesitated to kill some innocent people.