Now 24 years old, Cummock couldn't believe his eyes when he saw his father's murderer board a plane for his homeland of Libya.
"We were stunned and extremely angered," Cummock said. "It's as if the tragedy is continuing."
Cummock, who has a research job at the Miami Project to Cure Paralysis, said he was speechless.
"This is a man who was convicted of mass murdering 270 people and now he's just been released to go home to be welcomed as a hero, so we're really at a loss for words," he said.
He wasn't at a complete loss for words. Yesterday, he sent a letter to the Scottish Cabinet Secretary for justice, stating that al-Megrahi's release was "morally incomprehensible."
Cummock's mother, Victoria, became an outspoken advocate for aviation safety after the tragedy. Traveling in France yesterday, she said the family is still getting by.
"I'm very proud of him and I know his father would have been as well," Victoria Cummock said. "It's been quite a difficult life for the family members who've been left to pick up the pieces."
Matthew said he still misses his father after all these years.
"Even now, I'm still a young man and as I go forward in life, I'm still going to struggle without him being there," he said. "My father never came home from that flight, and I think it's absolutely ridiculous that al-Megrahi gets to go home."