When FBI Agent Donald C. Roberts was knocked off his chair during the shootout at the Singer compound, he thought he was hit by gunfire. But then he turned out to be uninjured.

Not until Wednesday did he find out a bullet had penetrated his jacket within a few inches of his heart.Roberts' testimony was the biggest surprise so far in the Singer-Swapp trial.

He said that on the morning of Jan. 28, the day of the shootout that killed corrections officer Lt. Fred House, he was stationed in a staging area to the west of the building occupied by House and other agents. Roberts, Salt Lake City, was in the kitchen of the Jepsen home, along with other FBI agents.

Peering through a window toward the Singer log house, he saw Addam and Jonathan Swapp head toward the goat pen, the event that precipitated the shooting. A state corrections officer asked for water for his police dog, and House got up to get some from the sink and returned to his post.

"I heard a loud explosion, gunshot, immediately in front of my face at the wall," he said. The shot blasted out plaster just under the window.

A cloud of powdery white material flew at his face and "I felt a sharp pain." He fell off his chair, crying, "I'm hit, I'm hit."

Another agent jumped on top of Roberts and searched for a wound. But he found none. His outer flight jacket had a small hole in the left chest, and the bullet-proof vest under it had a matching hole in it.

These holes were close to the heart, although a little to the left of it.

When the bullet-proof vest was examined with a metal detector a week later, nothing showed up. The assumption was that Roberts had been hit with a fragment of plaster or some other material from the house, or that it was such a tiny fragment of a bullet that it was undetectable.

On Wednesday, when he came to court, the outer jacket was put through an X-ray machine operated by security officers on the first floor of the courthouse. Through this machine officers run attache cases, handbags and anything else that could conceal a weapon.

What did the machine reveal?

It "found what appeared to be a bullet in the jacket," he said.

There in the courthouse, the jacket was cut open with a pocket knife. "And a bullet dropped out," Roberts said.

It had apparently gone through the wall of the Jepsen home, penetrated the jacket, gone into the vest, bounced back out and re-entered the jacket. The slug fell into the lining and was undetected until Wednesday.

Roberts displayed it to the jury, holding up a copper-jacketed bullet that looked larger than .22 caliber. It was to be tested overnight Wednesday by the FBI crime lab to determine which gun fired it.

FBI Agent Hal G. Metcalfe was also in the Jepsen house at the time. Watching through binoculars, he saw Addam and Jonathan Swapp leave the Singer home and walk toward the goat pen with a pail for the goat milk.

After they visited the goat, the brothers walked back into Metcalfe's view, heading to the Singer residence again. They were about three-quarters of the way there.

"I heard rifle fire, and I saw them duck and swing around," he said. At that time, the Swapps had their rifles slung on their backs.

"I moved the binoculars back toward the residence to see if I could see where the shots were coming from." But he saw nothing happening at the home's windows.

He looked back toward the Swapps, and was startled by what he saw.

"I saw Jonathan in a kneeling position pointing his rifle in my direction. . . . I told everybody, `Get down, get down, he's shooting at us.' "

He said, "I couldn't believe he was actually pointing it in my direction. . . . I didn't want to get shot."

Then, from his observation post, Metcalfe "saw Addam Swapp coming from the residence. He had a towel wrapped around his hand. He was staggering, tripped several times, fell, and then he went out of my view."

Addam Swapp had been shot by one or both of the FBI agents who had fired from the Bates house, wounded in the wrist and chest.

Half an hour later, the family surrendered.