TAMPA, Fla. (AP) - School officials have figured out where a bullet that was found on a school bus came from.

A student told authorities on Monday that he picked the bullet up from the ground on his way to school. It fell out of his pocket and was picked up by another student - prompting a modified lockdown of three schools in the Tampa area.

Because of the school shooting in Connecticut last week, Hillsborough County stepped up security and sent uniformed deputies to elementary schools on Monday.

Officials didn't find any other ammunition or weapons during searches of school buildings and students' belongings.

School officials had extra security on Monday due to the shootings at an elementary school in Connecticut.