Trump Shooter Thomas Matthew Crooks Official Cause of Death Released

Thomas Matthew Crooks -- the would-be assassin who tried and failed to take out Donald Trump -- now has an official cause of death in the books ... if it wasn't already obvious.

The Butler County Coroner tells TMZ ... Crooks died from a gunshot wound to the head, and the coroner is ruling his death a homicide. Of course, he was shot and killed by a Secret Service agent after he opened fire into the crowd in Butler, PA this weekend.

To be clear, "homicide" is the manner of death, and not a crime ... like murder or manslaughter. The coroner's ruling in no way suggests the Secret Service snipers were in unjustified in taking out Crooks ... who had not only opened fire on a former President, but also shot and killed a citizen in the crowd.

Remember ... we got footage of Crooks firing an AR-15-style rifle from the top of a building just outside Trump's rally ... with Crooks positioned only about 130 yards away from DT.

Crooks wounded Trump, killed one person and injured 2 others in the crowd ... before snipers killed him within a minute of him opening fire ... with a fatal headshot. There's a photo floating around online that purports to show his body in the aftermath ... and it certainly looks like what the coroner is telling us.

The photo in question is incredibly graphic and seems to have been taken by an official who attended to his body.

As we reported, 20-year-old Crooks also tried and failed to make his high school rifle team ... getting rejected because he was a terrible shot. Although, worth noting ... he's reported to have been part of a local shooting club regardless.