Police believe it was a case of a friend defending a friend.

A woman who took three people hostage at a Caterpillar factory Tuesday afternoon was apparently upset over a friend being fired by the construction equipment manufacturer.

Pam Arizona (search), armed with a shotgun and claiming to have explosives on her body, released her captives over the course of two hours before surrendering to officers. By early evening, investigators had found no evidence of explosives.

Arizona, 55, was jailed on $1 million bail early Wednesday, authorities said. She was charged with kidnapping and making false bomb threats.

"Apparently, she is an acquaintance or friend of an employee terminated recently" and was "demanding answers," said Johnston County (search) Sheriff Steve Bizzell. He described Arizona, who is not a Caterpillar employee, as "irate about the treatment that her friend got."

Negotiators brought in the friend to talk with Arizona, said State Bureau of Investigation agent Mike East. The friend said she was worried about Arizona's safety.

"Once she talked to her friend, she was at peace and she was able to come out," East said.

More than half of the plant's 800 to 900 employees were working at the time, officials said. They were removed on buses.

The hostages — two women and a man — were in the lobby when Arizona entered the plant southeast of Raleigh. They didn't know her, officials said.

"The thing we're thankful for is everybody's out, nobody's hurt," sheriff's department spokesman Pat LaCarter said.