It's only a murder if he would have survived the shots that knocked him down the first time. As Derec says, they were acceptable. He was out of his mind on PCP and attacking. You either contain (not feasible out in the open) or stop (up to and including firearms.)
He attacked...a car. Laquan McDonald's life had more value than car--or the car's tires. Even if he was black and even if he was high.
If he were 'out of his mind' then the shooting(s) are even less justifiable. There were multiple police officers and police vehicles present. There were multiple options that did not include firing 16 shots into Laquan McDonald.
There certainly were more options than lying which is the topic of this thread: the police lied. They falsified police documents. This is the topic of this thread and it's important no matter who was shot or why.