He seemingly died of heart attack, but is his death natural or was he murdered?

His parents seemingly died in ca. 1530 due to the plague.

When Larry seemingly died, Alan came into possession of the fear gas and other equipment.

Though Mai seemingly died (again) in the explosion, she was shown alive and well the very next day.

The fighter returns on autopilot, its pilot having died seemingly from old age.

John is hit by a car and seemingly dies on October 17, 2007.

Groot seemingly died buying his team some time to escape the battle.

She seemingly dies after her group fails to kill Warrior.

Jack rushed in and cradled Tony as he seemingly dies.

He died seemingly suddenly, but not from hostile or friendly fire.