Lioness was killed by another lion in zoo

I found this article on CNN

According to the article, a male lion killed other lioness while zoo visitors watching lions. After the accident, the lion killed other lion and other family members were took from the zoo.incidentStaffs in the zoo said that this case is really rare and merely happened. He said he has worked for 35years but he never experience this incident.

I was surprised at the news when I found the article. As mentioned in the article, visitors thought lioness just played together, but they realized that actually a lion killed another lioness!! Staff said they don't know why that terrible case happened. I am very sorry to the lioness who was killed and his family.   If this case occurred by human, absolutely who killed somebody would be punished. However, it is difficult to do same thing to animals. In fact, 3days later, the lion who occur incident was put back to the zoo.I worry if he do same thing again...

☆ why do you think the incident happened?

☆ when accident like this case happened, how do you think people  should do or deal with animals?