CLAYTON, Mo. -- A high school senior will spend two months in jail for an explosive senior prank that his teachers didn't find so funny.

Prosecutors say 18-year-old Benjamin Smith fashioned a crude explosive device and detonated in an empty locker near Oakville High School's cafeteria in suburban St. Louis on April 19. The locker was dented, and no one was injured.

The St. Louis Post-Dispatch reported Wednesday that Smith's attorney, Pat Conroy, called the explosion "a stupid senior prank that went awry" and said that Smith "has accepted responsibility for what has happened."

Smith pleaded guilty Tuesday to misdemeanor charges of property damage and recklessly causing an explosion.

Smith originally faced felony charges, but had the counts reduced as part of a plea agreement between Conroy and St. Louis County prosecutor Paul Stuart. If prosecutors had pursued the felony counts, the penalty could have been 11 years in prison.

Associate Circuit Judge Gloria Clark Reno accepted conditions of the deal and imposed the 60-day sentence without comment.

Conroy said the same prank "20 to 40 years ago would have been treated differently than this day and age."

But St. Louis County Prosecuting Attorney Robert P. McCulloch said such crimes can't be written off as childish behavior.

McCulloch called the explosion "absolutely stupid," but said, "as tragic as these cases could have been, I take them very seriously."

The prank came just three days after a gunman killed 32 people at Virginia Tech university and one day before the anniversary of the shootings at Columbine High School in Littleton, Colo.

McCulloch said the explosion was comparable to false bomb threats that his office also takes seriously. There was a rash of such threats throughout the St. Louis area last month.

Prosecutors say Smith mixed chemicals in a 20-ounce plastic bottle to create the explosive at the school. He was suspended over the prank and allowed to graduate -- although he was not allowed to attend the commencement ceremony with his peers.

Conroy said that with good behavior, Smith could be released from jail within 48 days.