NPR News

Two explosions rocked the finish line of the Boston Marathon this afternoon, leaving at least three dead and dozens injured, the Boston Police Department reports.

The explosions happened in quick succession four hours after the beginning of the race, the world's oldest and one of the most prestigious road races in the world. At that point, the majority of 27,000 runners had crossed the finish line. Thousands, however, were still out on the course.

In 1957, Joel Healy witnessed one of the largest nuclear tests ever conducted on U.S. soil.

Healy was in the U.S. Army, stationed in the Nevada desert north of Las Vegas at Camp Desert Rock. He was 17 years old and a private first class at the time.

Healy drove dump trucks, moved materials, and built structures, like houses, that would be destroyed by the explosions so the Army could study the effects of a nuclear blast. He also helped build the towers where many of the bombs were detonated.