Tune in Sun., April 17 at 9 p.m. ET

April 19, 1995: 168 people are killed and hundreds more are wounded when terror strikes America's heartland.

At the time, the Oklahoma City bombing (search) was the worst terror attack on American soil and launched a massive investigation. After agents conducted over 28,000 interviews, followed more than 43,000 leads and collected nearly 3.5 tons of evidence, the plotters were uncovered. Timothy McVeigh (search) was convicted and put to death, claiming he did it by himself. Terry Nichols (search) sits in jail for the rest of his life and hasn't talked publicly.

But were they really acting alone?

Some senior FBI agents believe that coincidences and conflicting evidence suggest more to the plot than the government presented during the trials.

Did the government close the door too quickly on some key pieces of evidence? Was there a Mideast connection? Did the ATF ignore warnings? And, could a congressional investigation be right around the corner that could finally provide answers once and for all?

This weekend, FOX News presents, "The Oklahoma City Bombing: Unanswered Questions."