People.comCrime High School Football Player Dies in Dad's Arms After NFL Star's Brother Allegedly Shoots Him The 18-year-old suspect's attorney claims he fired in self defenseByChris HarrisChris HarrisTwitterChris Harris has been a senior true crime reporter for PEOPLE since late 2015. An award-winning journalist who has worked for Rolling Stone and MTV News, Chris enjoys prog rock, cycling, Marvel movies, IPAs, and roller coasters.People Editorial GuidelinesPublished on August 5, 2022 02:04 PM Share Tweet Pin Email Isaiah Hernandez.Photo: Go Fund Me A suspect has been accused of murdering a Florida teen on Tuesday during an alleged drug deal gone bad in Little Havana. Online records confirm Demarcus Cook, 18, was arrested Wednesday on a single count of first-degree murder. According to Miami Police, 17-year-old Isaiah Hernandez was standing outside his home when Cook allegedly drove up to him in his Jeep Grand Cherokee. Police allege that Cook was there to purchase marijuana from Isaiah. However, there would be no exchange of cash. Instead, detectives allege Cook intended to steal the marijuana from Isaiah, and allegedly opened fire on the teen from inside his Jeep. Isaiah's father, Orlando Hernandez, told WSVN he was home at the time, and heard five shots followed by screaming. "I came outside, my son on the floor, gushing with his last breath — was his life, and you, as a parent, can't do nothing but try to save him, and you don't succeed," Orlando Hernandez told the station. Police searched Cook's home, and allegedly recovered the gun used in the murder as well as the stolen marijuana. Miami-Dade Corrections Cook, according to the Miami Herald, is the half-brother of Minnesota Vikings running back Dalvin Cook. In 2019, when he was 14, Demarcus Cook and another teen were shot while playing basketball in Little Haiti, WPLG reports. According to WTVJ, Cook's attorney claimed he fired on Isaiah in self-defense. Cook remains in jail on no bond. He has not entered a plea to the charge against him. Want to keep up with the latest crime coverage? Sign up for PEOPLE's free True Crime newsletter for breaking crime news, ongoing trial coverage and details of intriguing unsolved cases.A GoFundMe campaign has been launched to help cover the slain teen's funeral expenses. Isaiah played football for Miami Jackson Senior High School, where he was about to enter his senior year. The boy's dad said he was a great son who had a big heart, according to WSVN. "He was in school, and he played football," said Hernandez, noting Isaiah died in his arms. "You ask him for something, and he'll give it from his heart. You ask for his last dollar, and he'll give it to you." Speaking to WTVJ, Hernandez called Isaiah "a big bear with a big heart" who "wanted to do something in life, do better in life."