Michael Gargiulo: The serial killer next door?

"48 Hours Mystery" report helps Chicago detectives charge suspect in an 18-year-old cold case after new witnesses come forward

It happened nearly two decades ago, but to this day, Doug Pacaccio is still haunted by the moment he found out his sister, Tricia, had been savagely murdered.

"I just remember waking up to this, this blood-curdling scream of my father. ...And it was, 'Doug, call 911! Doug, call 911!" he said. "I don't really want to describe the details of what I saw. I have nightmares about it all the time."

Years later, while investigating Ashley Ellerin's murder, California detectives were surprised to learn their No. 1 suspect, Michael Gargiulo, was closely connected to another murder in his hometown of Glenview, Ill.

"Like any high school girl, she was boy crazy. We all were. We, we'd talk about boys for hours... We had a wonderful time in high school," friend Karen Jones said of Tricia Pacaccio.

She will never forget the last time she was with Tricia. It was an unusually cool and foggy August night in 1999. It was Friday the 13th.

"That night, a whole group of us got together for a scavenger hunt party and we all had dinner at a restaurant ...for one of the final parties of the summer before we all went off to college," she said.

Tricia got home sometime after 1 a.m. With keys in hand, she went to the side of the house to let herself in. She never made it.

The next morning, Tricia's father, Rick, found his daughter.

"I woke up and had a cup of coffee, and I was goin' out to my van," he said. "And I just happened to see two little tennis shoes stickin' up by the side door. And when I saw it was her, I dropped the coffee cup...

"I tried to revive her," he said, crying. "That is the worst feeling in your life, when you can't do nothin' for somebody you love."

Tricia's mother, Diane, was at work. "And I just left work and jumped in the car and came home and I don't remember anything else," she said.

Ray Salihovich was the first uniformed police officer on the scene.

"She had a lot of blood on her shirt or her blouse," he recalled. "I was guessing she was stabbed numerous times.

"I heard a lady screaming," Salihovich continued. "I turned and looked 'cause I was still in the front yard and the mother was running toward Trish. And I basically tackled her. I didn't want her to see Trish like this and remember her daughter like that."

Homicide detectives from the Cook County Sheriff's Office quickly took over the crime scene.

"The crime scene back then," Salihovich said, "I thought it could have been handled better, taped off more."

"You think there were mistakes made that day...that hindered the investigation?" Maher asked.

"I think the crime scene should have been handled a lot better. More secure. Yes," he replied.

While investigators were trying to secure the scene, one young neighbor was paying close attention: 17-year-old Mike Gargiulo.

"I called him. I'm like, 'Hey, you know, what's going on? It's like, 'I know it's crazy,'" said Scott Olsen, who was childhood friends with Gargiulo. "He goes, 'Yeah, I went over there.' He goes, 'You couldn't miss all the sirens and everything, all the commotion.'"

"What was Mike's reaction to all of this?" Maher asked Olsen.

"It was equal to mine," he said. "Just shock. Complete and total shock."

"It seemed appropriate at the time?"

"Absolutely."

Olsen says he met Mike through Doug Pacaccio. "He grew up in their house," he says.

Just two days before her murder, Olsen and Gargiulo had given Tricia a ride to her boyfriend's house.

"We just drove her. She wasn't in the car very long. She got out," Olsen recalled. "And that was the last time, I guess, we saw her."

Asked of Tricia and Gargiulo had any kind of a relationship, Olson replied, "Same as it was with me... You're my little brother's friend."

Scott Olsen says there were two sides to Michael Gargiulo. One side was an awkward, insecure teen.

"The other side of Mike was, he had what I called a crazy switch, where if he really wanted something, he was gonna get it, one way or another. And he flipped a switch all emotions gone," he said snapping his fingers.

Yet nothing about Gargiulo gave the Pacaccios cause for suspicion.

"I knew him to be very quiet and, like, one of the guys in the back," Rick said. "Was never loud or boisterous whatsoever."

The Pacaccios say they never saw him display any aggressive or violent behavior. Asked if Gargiulo was friends with Tricia, Rick and Diane both say "no."

But starting about a year after Tricia's death, Gargiulo began drawing attention to himself with some strange behavior.

"It first started with the flower," said Diane.

"He bought Diane flowers," says Rick.

"I'm like, 'Why is Michael bringing us -' it was live greenery," Diane continued. "At Easter time, he bought us a lily. He bought us [a] dinner certificate to a restaurant. ...And then he even brought [Rick] a shirt."

"It's like, wait a minute, nobody else is giving gifts," said Rick.

"And I said to him, 'Why is Michael giving us all this stuff?'" said Diane.

"And we were tellin' the detectives at the time what was going on," Rick told Maher.

It was enough for Cook County Sheriff's Detectives Jack Reed and Mark Baldwin to take a closer look at Michael Gargiulo.

"One of the psychologists that was talking to us says, 'He's trying to expiate his sin. He's trying to atone for his crime with the presents that he was giving the family."

The detectives discovered Gargiulo had a criminal record, having once been arrested for theft. Then Doug Pacaccio told them about a curious conversation he once had with Mike.

"He looked at me and he said, 'If you knew who did this, would you kill them?' I said, 'Well, what do you think? Ask any father, any brother... I think you know the answer," he said. "The police called me later on - Det. Jack Reed - and said, 'Do you realize Michael Gargiulo called us and told us that you threatened him?'"

According to Det. Jack Reed, "He knew how to play the system, OK? He knew the heat was on."

And it seems that Gargiulo wasn't shy about pointing the finger at his friends.

"When we were finally able to compel Mike Gargiulo to talk to us, he was aware that we had shown interest in one of his good friends, Eric Agazim," said Det. Mark Baldwin.

Eric Agazim was another kid from the neighborhood and a close friend of Gargiulo and Doug Pacaccio... but not so close that Gargiulo wouldn't give him up to the detectives.

"He attempted at that time to lay all the suspicion on his doorstep by telling us that the morning after the murder, Eric came to his home and asked him to come along so he could hide something... a gym bag," Baldwin said. "We asked Mike Gargiulo what was inside the bag. [He said] 'I have no idea.'"

Maybe... but the detectives say Gargiulo strongly implied it contained the murder weapon: a knife.

"Did you get the feeling he was intentionally steering you towards Eric?" Maher asked.

"He did," Det. Reed replied.

Gargiulo's story worked. When Agazim refused to talk with police, he became their No. 1 suspect.

But police were unable to develop any real evidence against Agazim, Gargiulo or any other suspect for that matter. The Tricia Pacaccio case gradually went cold. Then one afternoon, five years after Tricia's murder, Michael Gargiulo suddenly showed up on the Pacaccios' doorstep.

What he did next convinced Tricia's parents that he had murdered their daughter.

"He says, 'I need to talk to Rick,' and I said, 'Well he's at work Michael.' And he says 'Can I wait?' And I say, 'Yes,'" Diane Pacaccio recalled. "He sat and waited for over an hour for him to come home from work...sat at my kitchen table."

"I remember walkin' in the garage door...and I looked at him, and he had this look on his face like he was gonna say something to me," Rick said. "The garage door opens, his father and one of his sisters come in, and say, 'We have to leave, Michael.' And they pick him up and whisk him out."

"You believe that was the moment that you started to think Michael Gargiulo may have had something to do with her death?" Maker asked.

"Oh there was no doubt about it," said Rick.

Rick Pacaccio called the sheriff's detectives to tell them Gargiulo was their man. But it was too late.