What must it be like to know that your son is like adam lanza -- the troubled loner responsible for the horrific massacre at sandy hook elementary school?
Sadly, this father knows all too well. His son killed five people in another mass shooting in May.
Now, the killer's father, Walt Stawicki, is speaking out about what it's like to have a son who's a mass murderer whose evil deeds shock the nation.
Walt told INSIDE EDITION's Megan Alexander, "Something took him over that day. He had a monster in him that morning."
He's just like Peter Lanza, the father of Adam Lanza who slaughtered those 20 innocent little ones and their six teachers in Newtown, Connecticut.
Alexander asked Walt, "What is Peter Lanza, the father, going through?"
Walt replied, "He may be in shock at this point. He may be suicidal at this point. Or he may be going through, 'Well, you know, it wasn't me.' "
There appear to be eerie parallels between Ian Stawicki and what we know about Adam Lanza. Ian Stawicki had been suffering from mental illness for years and had become sullen and withdrawn. But his father says he never saw his son's senseless rampage coming.
"That's what I've learned—by the time you see things are going downhill, it can be over the cliff, down and done," said Walt.
Cops say Ian Stawicki became enraged when he was ordered to leave the coffee shop after getting into an argument with a customer a few days earlier.
He shot four people dead inside the shop, then killed a woman out on the street as he tried to hijack her car. A witness called 911.
911 Operator: "911, what are you reporting?"
Caller: "Man with gun assaulting woman on Eighth. Oh my god, he just shot her! Oh my god, he just shot her!"
Walt Stawicki says his son was obsessed with guns, just like we're hearing about Adam Lanza. He's criticizing Adam's mother, Nancy, for having guns anywhere near her troubled son.
"Why would she be tempting him. It's like leaving matches and flamethrowers and saying, 'I think my son might be a pyromaniac,' " said Walt.
Just like the Sandy Hook killer, Ian Stawicki took his own life as cops closed in on him. Now, his father has this urgent message for parents with children whose severe mental problems could lead them to kill.
Walt said, "Find help and do it as soon as you can. Do it today."