Chief James Moran led the investigation. He firmly believed that List should not be allowed to escape the consequences of what he had done. Every effort would be made to track him down and bring him to justice. Within an hour of the discovery of the bodies, a teletype alarm was sent out for John Emil List. Then the bodies were removed for autopsy and shell casings were picked up to try to determine how many times the victims were shot at and not hit.
It came out later that List had numerous books on how to commit murder and get away with it, and that he had spoken about how easy it would be for an accountant like himself with access to social security numbers to assume a new identity. He also had developed an obsession with military strategy games, making himself a winner when he could not succeed in the real world.
His missing blue Chevrolet Impala was located at Kennedy International Airport in long-term parking. The voucher was dated November 10th. He was not listed as having taken a flight, but his passport was missing from the house. The trail ended there and the FBI was given jurisdiction. In absentia, List was indicted by a grand jury on five counts of murder and on fleeing a crime scene across state lines.
His records showed that he had failed miserably as an insurance salesman and was several thousand dollars in debt. He was behind on his mortgage and utility payments, and had made less than $5000 for the entire year. He owed his mother $10,000 for payment for his house, and foreclosure proceedings had already started. He had taken all of his mother's savings as well, some $200,000.
As people were questioned, it became clear that List not only had a troubled marriage to a wife who despised him and who was growing increasingly ill and house-bound, but also that he was caught between her and his overprotective mother.
The children clearly had been disturbed, showing signs of fear and panic in the weeks before the day of the murder. Patty had even told her drama coach that should he hear that they were about to go off on a vacation that would be the signal that her father was about to murder them. Illiano had not taken this seriously.
As bullet patterns in the bodies and the walls were examined, along with blood spatters and the evidence of attempts to clean up, police were able to roughly determine all of the events of that day and List's preparations for it. List had made sure that deliveries of newspapers, mail, and milk had been stopped. (The milkman did come that day, but read the note on the door and left nothing behind.) He had also mailed a special delivery letter to himself containing a key to his file cabinet. Then on the morning of November 9th, he waited until the children left for school, knowing that he would kill them later in the afternoon when they returned home.