Best Friend ‘Ruined My Life’ When He Killed His Own Parents

April 4, 2014— -- Michael Mandell, whose best friend, Tyler Hadley, is in prison for killing his own parents before throwing a house party, said his life was ruined because of the murders.

“It ruined my life. It ruined Tyler's life. It ended his parents' life,” Mandell, 20, told ABC News’ “20/20.”

“I can't go to school without people saying, ‘That's Michael Mandell,’ and relating me to something this sick. And that's what everyone knows me as ... the best friend of a murderer.”

On July 16, 2011, Tyler Hadley, then 17, bludgeoned his parents, Blake and Mary Jo Hadley, to death with a hammer at their home in Port Saint Lucie, Fla. After cleaning up the blood, he then had a house party that night, while his parents’ bodies remained in their bedroom.

Mandell grew up just a block away from Tyler Hadley. “I was just walking around, looking for friends, and I met Tyler … He slowly became my best friend,” Mandell recalled.

When Hadley was 15, his family said they began to see a change in him.

“He started skipping school, hanging out with the wrong crowd, getting on drugs,” Tyler Hadley’s aunt, Cindy Hadley, told “20/20.” “We knew marijuana.”

By the time their son was 17, Blake and Mary Jo Hadley had tried everything to get their son on track, including a psychiatrist, antidepressants and an outpatient mental health and substance abuse program, but nothing changed.

After Tyler Hadley came home drunk one night, his parents took away his phone and car. “He felt that, I guess, that was too much, and that she was over disciplining him. And he said he wanted to kill her,” Mandell said.

To Mandell, it didn’t seem like Hadley would actually do it. “It sounded like he was mad he was getting punished,” he said.

Just a week before the party, Tyler Hadley’s parents took him on a family reunion to a cabin in Georgia. “I never saw Tyler lose his temper, ever,” Cindy Hadley said. “That's what is so bizarre about everything.”

The day of the murders, Hadley posted an invitation on Facebook to a party at his house. Mandell said Hadley told him that his parents were away in Orlando, Fla.

“Young people [were] drinking and sitting around talking. But, the weird thing was, most people in there, Tyler didn't even know,” Mandell said of the party.

READ MORE: Teen Took Selfie With Best Friend After Learning the Friend Was a Murderer

During the party, Tyler Hadley pulled Mandell aside and told him he needed to tell him something, so the two went outside to talk.

“He says, ‘Mike, I killed my parents.’ And I said, ‘No you didn't, Tyler. Shut up. What are you talking about?’" Mandell said. “And, he said, ‘Mike ... look at the driveway, all the cars are there. My parents aren’t in Orlando. I killed my parents.'”

Mandell said he went inside and saw blood by a computer desk and more blood by the master bedroom door, but he thought Hadley was playing a prank on him and still didn’t believe he killed his own parents.

“I took Tyler into the garage, and I said, ‘What's going on here? I want to see them dead, if you really did it. I don't believe you,’” Mandell said.

He said Hadley told him the party needed to die down before he could show him the proof, but Mandell refused to wait and went to check for himself.

“I come up to the [master bedroom] door. The party's going on over here, and I turn the door knob,” Mandell said. “I looked down, and I [saw] his father's leg against the door … My eyes popped up, and I said, ‘Oh my, he's telling the truth. He did it. This is real.’”