In the video posted online, there are no Gardaí on the scene and it looks like there are about 8 security guards around the suspect. 4 to 5 men are holding him down, the large white bald bloke is using what looks to me, like unreasonable force, especially around the suspect's neck and skull. The black security guard and other colleagues are restraining him with reason.
I think there's a solid case here for involuntary manslaughter. It looks like he died from positional asphyxia. That big bloke dropping down with his knee, then covering the suspect's head with his hood, restricts their ability to breathe, is criminal and totally disproportionate to the alleged crime of shoplifting.
I wouldn't be surprised if the shop/security company is liable for his death.