High school student Alex Browning boards VolĂŠe Airlines Flight 180 with his classmates for their senior trip to Paris, France. Before take-off, Alex has a premonition that the plane will suffer a catastrophic engine failure, causing the plane to explode in mid-air, and killing everyone on board. When the events from his vision begin to repeat themselves in reality, he panics and a fight breaks out between Alex and his rival, Carter Horton. This leads to several passengers being removed from the plane, including Alex; Carter; Alex's best friend, Tod Waggner; Carter's girlfriend, Terry Chaney; teacher Valerie Lewton; and students Billy Hitchcock and Clear Rivers. None of the passengers, except for Clear, believe Alex about his vision until the plane explodes on take-off, killing the remaining passengers on board. Afterwards, the survivors are interrogated by two FBI agents, who believe that Alex had something to do with the explosion.
Thirty-nine days later, the survivors attend a memorial service for the victims. That night, Tod is killed when a chain reaction causes him to be strangled in his bathtub. His death is deemed a suicide; however, Alex does not believe that Tod killed himself. He and Clear sneak into the funeral home to see Tod's body, where they meet mortician William Bludworth, who tells them that they have ruined Death's plan, and Death is now claiming the lives of those who were meant to die on the plane. The next day, Alex and Clear discuss what the mortician said at a cafe. Alex believes that if they look out for omens they can cheat Death again, although Clear is skeptical. They encounter the rest of the survivors; and when Carter provokes Alex, Terry storms off in anger and is suddenly killed by a speeding bus.
After watching a news report on the cause of the explosion, Alex realizes that the survivors are dying in the order they were meant to die on the plane. He deduces that Ms. Lewton is next and rushes to her house to ensure her safety. Thinking Alex is up to no good, Ms. Lewton calls the FBI agents, who take him in for questioning. Although Alex is unable to convince the agents of what is happening they decide to let him go. Nonetheless, he is too late to save Ms. Lewton, whose house explodes after she is impaled by a falling kitchen knife.
The remaining survivors reunite and discuss what to do while driving through town. During the discussion Carter learns that he is next on Death's list. Frustrated over having no control over his life, Carter parks his car on railroad tracks, wanting to die on his own terms. He changes his mind at the last minute; but cannot get out when his seat belt jams. Alex manages to save Carter when his seat belt rips, just before his car is smashed by an oncoming train. As Billy warns the others to stay away from Carter he is suddenly decapitated by flying shrapnel from the car wreckage.
Alex deduces that since he intervened Death skipped Carter and moved onto Billy, and realizes that he is next on Death's list. While hiding out in a fortified cabin Alex recalls switching seats with two girls in his premonition, meaning Clear is actually next, and he rushes to save her while being chased by agents. Meanwhile, Clear is trapped inside her car with a leaking gas tank, surrounded by loose live wires. Alex arrives in time to save Clear and grabs the wire, allowing her to escape from the car seconds before it explodes, leaving Alex incapacitated.
Six months later, Alex, Clear, and Carter travel to Paris to celebrate their survival. While discussing their ordeal, Alex explains that Death never skipped him. After seeing more omens he leaves the table, and is almost hit by a bus, which swerves and crashes into a large neon sign that swings down towards Alex. Carter pushes Alex out of the way at the last second, and Alex says that Death has skipped him. When Carter asks who is next the sign suddenly swings back down towards Carter, implying that Death's plan is still in action.

Question: Who was investigating the explosion and Alex's premonition?
Answer: The FBI.
Alternative answer: the FBI