By Sharon Reich

MIDLAND CITY, Alabama (Reuters) - Bomb technicians on Wednesday ended their sweep of an underground bunker where an Alabama boy had been held captive for nearly a week and authorities said no additional explosives were discovered beyond those found after the raid to free the boy.

The FBI's declaration that the scene of the standoff was now safe came as the boy celebrated his sixth birthday and local officials collected birthday cards on his behalf.

In all, authorities discovered two explosive devices.

One was inside the bunker where Jimmy Lee Dykes, 65, had holed up with the boy he had randomly snatched off a school bus after killing the driver. The second device was in a plastic pipe that negotiators used to communicate with Dykes during the standoff near Midland City in southeast Alabama that ended on Monday.

"Evidence recovery has begun," FBI spokesman Paul Bresson said on Wednesday, adding it would likely take several more days to process the crime scene.

FBI agents stormed the homemade bunker and shot and killed Dykes on Monday after surveillance equipment showed him wielding a gun and looking agitated, law enforcement sources said. The boy was rescued unharmed.

A preliminary investigation indicated Dykes "engaged in a firefight" with SWAT team members who entered the bunker, the FBI said.

Dykes appeared to have reinforced the bunker to thwart entry attempts by law enforcement, agents said, without revealing further details.

The drama came against a backdrop of debate about gun violence and school safety across the United States, following the shooting deaths of 20 children and six adults in December by a gunman who had forced his way into a Connecticut elementary school.

The rescued Alabama boy, identified only as Ethan, turned 6 on Wednesday. Relieved residents posted signs around his hometown with messages such as "Happy Birthday Ethan" and "Welcome Home," and trash bins were set up to collect cards for him. Continued...