A good Samaritan armed only with a pocketknife stabbed a dog to death as it was attacking a 77-year-old woman in her front yard, officials said.

Ann Lyon, who was with her own dog when the other dog attacked Sunday afternoon, was wearing a leather coat and was spared serious injury, authorities in Council Bluffs said.

"I just heard her screaming 'Help! help me! help me!' so I ran over and tried pulling it off her," passer-by Kevin Daub, told Omaha, Neb., television station WOWT. He said he was tiring after struggling for a minute, so he pulled out his pocketknife and killed the dog.

Lyon told KETV of Omaha, Neb., that she felt Daub had no choice. "It wouldn't quit. It would not quit, and he was hitting it with his fists and it still wouldn't quit," she said.

Galen Barrett, Council Bluffs chief animal control officer, said the American bulldog was properly licensed and had not caused any problems before it got off its owner's property.

"I don't know what tripped it," he said. It's unclear if the dog was after Lyon's dog, which he described as a young Rottweiler mix, he said.

Lyon estimated the attacking dog weighed about 90 pounds, but didn't know about the size of Daub's knife.

The dead dog was to be tested for rabies.

The name of the dog's owner, who lives in the same neighborhood as Lyon, was not released. The investigation was continuing, Barrett said. He said charges, if filed, could range from a dog at large to harboring a dangerous dog, both misdemeanors punishable by fines.

Authorities said Lyon didn't require medical care. Her dog also was uninjured.

"I talked to her this morning," Barrett said Monday. "It's an issue of bruises rather than punctures."

Said Lyon: "The only thing I could think of was covering my dog so he wouldn't kill her."