Spoilers for TV Show - Invincible (Amazon Prime)
At the end of the first episode,
Omni-Man lures the Guardians of the Globe into their HQ. He then fights them by himself. This seems to be a hard task even for Omni-Man, as he gets beaten by the Guardians multiple times, wounding him heavily. Eventually he manages to kill all of them, but his wounds and fatigue make him drop to the floor. The GDA (Global Defence Agency) arrives at the scene shortly afterwards, and Omni-Man is taken into their hospital, where he spends a week or more in a coma, implying he suffered a lot of damage. All of the Guardians are declared dead and the GDA suspects someone from outside attacked, and managed to kill them, but not Omni-Man.
His reasons for doing that are revealed in the Season 1 finale. However, it feels out of character for him to carry out the deed all by himself. Also, his species (Viltrumites) are mentioned to be super intelligent and resourceful. His being at the scene of the incident is an instant reason for someone to doubt him (this is proven right, as that's how Art Rosenbaum later identifies Omni-Man as the culprit). There are many other ways he could have done that without getting himself involved.
Luring them into the HQ and demolish it with a bomb, for example? Then finish off the ones who are alive?
Why take the hardest path?