Yellowstone National Park officials continue to probe the misguided attempt by two people whose actions caused the euthanization of a bison calf, a park spokeswoman said Monday.

"What I can tell you at this point is that investigation is ongoing," Morgan Warthin said. "Law enforcement is continuing to look into the incident."

And park officials faced a tough decision after the calf could not reunite with its mother and the herd, Warthin said. Mother bison sometimes reject their offspring, but the human interference made the situation much worse.

The calf was causing dangerous traffic situations because it was approaching cars and people, she said.

Rangers considered several options with the weakened calf including sending it to slaughter, sending it to research, or leaving it alone to die, Warthin said.

"Because the bison had not fed likely for a day-and-a-half, we would just allow the natural ecological processes of Yellowstone to take place, and because the bison had not eaten we would allow nature to take its course," she said. "The decision was made to euthanize the calf."

The case began May 9 when a father and son from a foreign nation were visiting Yellowstone in the Lamar Valley in the northern area of the park when they saw a newborn bison that appeared cold to them, she said.

They put it in their vehicle and drove to the Lamar Buffalo Ranch in the Lamar Valley in the northern area of the park to give it to rangers, Warthin said. They did it, she said, "because of their misplaced concern for the animal's welfare."

Park rangers tried several times to reunite the calf with the herd, but the herd rejected it, she said.

Rangers also cited the man and his son, Warthin said. "They were given a fine for $110, and they were cited for wildlife protection."

The federal regulation about "wildlife protection" includes the taking of wildlife, and feeding, touching, and teasing wildlife, she said.

Warthin declined to say if father and son were ejected from the park, but did say the fine and citation may be only the initial law enforcement actions.

Because the case remains under investigation, park officials are not releasing the names of the individuals nor their country until it has been completed, she said. "This is such kind of a quickly evolving situation."

Wyoming U.S. Attorney Office spokesman John Powell said this is a federal, not a state or local case because it is in a national park.

Most crimes charged in Yellowstone Park are misdemeanors, such as driving under the influence, drugs and assaults. Even thought they are misdemeanors, they are still federal crimes.

Park Service rangers bring citations to the U.S. Attorney's Office, which then decides whether to prosecute those cases, Powell said. "In most cases we do because we feel that they cite people in an appropriate manner for appropriate things."