The motive still remains a mystery and many wonder why a Michigan State graduate who had worked in environmental sciences as a geologist, according to The Associated Press, would allegedly fire at passing motorists.
Casteel's relatives talk of mental problems that he suffered. His mother, Lana Hunt, told the Detroit Free Press that she worried he was mentally ill, but that he refused to get help, while Casteel's aunt told the Detroit News that he was paranoid that the government was after him.
"There was some statements made by family members with respect to his mental health and we're looking into that as well," Livingston County Prosecutor David Morris said Wednesday.
Secret Service chief psychologist Dr. Marisa Randazzo told "Good Morning America" that Casteel told his mother that if anything happens to him, the government may be involved. She said that this kind of paranoid thought can be a clue as to what may have been motivating him.
"There's so much we don't know about this case and that we're learning as this investigation unfolds," she said. "But we've got two big clues with what the mother and his aunt shared with newspapers, about this paranoia, about 'if anything happens to me, the government is to blame.' This suggests he may have been experiencing what we call a break with reality, which may have been part of a developing mental disorder like a psychosis."
Randazzo said that most people who develop this type of mental disorder don't engage in violence. Under stress -- like dire financial conditions, loss of a job -- people can develop this break with reality at some point.
"What's critical here is that law enforcement or the criminal justice system can play a key role in getting someone like this into treatment and back on track. These are treatable conditions," she said.