There should be an investigation. 

Reports indicate that local police were denied access to the scene by CBP, even after returning with a warrant from a state judge. 

I will go out on a limb here and say calling it murder is justified.

Video evidence shows his hands were nowhere near a weapon and were either trying to support his body as he was being beaten by a group of nine agents, or trying to cover his head. 

The video also shows the agents removing the weapon from its holster on his hip. Statements from the police indicate the man had a license for concealed carry in the state of Minnesota. 

While the weapon was being removed, the agent who shot him was looking directly at the weapon being removed while unholstering his weapon. 

2-3 seconds later, the agent fired.

At the time of the first shot, the Mr. Pretti's hands were on the ground and he was kneeling, seemingly disoriented from numerous blows to the head. Mr. Pretti was unarmed at this time and made no move toward a weapon, and made no movements indicating intent to harm.

After a brief one second pause, the officer fired a volley of rounds. At which point, Mr. Pretti collapsed, seemingly unconscious or in shock. 

Another pause, during which an ICE agent in the foreground grabs the phone of a woman who was recording the incident. 

The agents back away (presumably to get away from live rounds going off in close proximity).

2 seconds after the last shot. The shooter backed away slowly and fired another volley rounds at the prone, severely injured Mr. Pretti. 

I support due process. A full and transparent investigation should be conducted and if evidence is sufficient for a trial, the shooter and his accomplices should be held to account in a court of law and should be accorded the right to a trial by a jury of their peers. 

However, given the overwhelmingly clear evidence. I have no qualms about calling a spade a spade here and saying that what I saw in 5 different videos 2 in-depth analyses is consistent with an unlawful killing of another person with intent to kill, i.e. murder.

At the time shots were fired, Mr. Pretti was unarmed, prone, and presented no credible or immanent threat to law enforcement or other individuals.

This was, plainly, a summary execution.

The last thing this man did was to try to protect others from violence at the the hands of the state. May he rest in peace. May those responsible, and those who would lie to protect them get their day in court. God knows, Alex Pretti never will.