A California father allegedly confessed to killing his two young sons, mother, father AND the family dog because it was his "destiny" to do so.

Nicolas Holzer, 45, was arrested at the home he had shared with his 10-year-old son Vincent, 13-year-old son Sebastian, and his parents. On Monday night, he reportedly called police and calmy told them he had stabbed his entire family to death. The man had no prior criminal convictions and, though divorced from the mother of his children for eight or nine years, had received full custody of his sons, making the motive behind his actions an even greater mystery.

Police say the man explained to them that he first killed his 73-year-old father, William Holzer, in the den. Next, he said, he entered the bedroom his sons shared and fatally stabbed them while they slept. He then killed his 74-year-old mother, Sheila, in the hallway, before killing their Australian Shepherd dog. Police say they were able to recover two kitchen knives that they believe were used to kill each member of the family, all of whom suffered from multiple stab wounds.

When detectives arrived, Holzer allegedly claimed he had murdered his family to fulfill what he thought to be his destiny in life. He didn't provide additional details, but stressed that he "had to" do it, according to a police statement.

Police say Holzer's mental state will be a consideration as they continue their investigation.

Holzer has been charged with four counts of murder and animal cruelty. He is being held without bail.

We've heard of quite a few cases lately in which a father or mother murders his or her entire family and then commits suicide. Sometimes we discover this was done because the killer wanted to take revenge on another member of the family. This case is even more perplexing because Holzer had custody of his sons and was fortunate enough to be in a position to help take care of his own parents.

Why do you think this father would murder his entire family?