Last Person to Speak to Riley Strain Gives Statement, 'Huge' Development

The last person known to have spoken to Riley Strain before he disappeared has finally given a statement to the cops ... and his family is hailing it as a "huge" development.

Chris Dingman , a spokesperson for Riley's devastated family, told NewsNation the new witness spoke with the family first, and then "told the detective his account of the story of what happened to Riley” -- all this 3 weeks after they found his body .

Dingman didn't say who the witness was or share the specific details they provided about what happened to Riley ... before he disappeared and was later found dead.

As you know, questions have arisen over the nature of Riley's death because he didn't have his cowboy boots, pants or wallet on him when his body was pulled from the Cumberland River -- which was 2 weeks after he vanished from Luke Bryan 's bar in Nashville on March 8.

Dingman says Riley was definitely wearing all those items the night he disappeared ... which has the family thinking his death wasn’t just an accident.

On top of that, the preliminary report confirmed the absence of water in his lungs ... raising further concern he might've already been dead before hitting the water, and casting doubt on the assumption he drowned.

Riley's family went ahead and ordered a second private autopsy from an independent company to try to clear up all those lingering questions about his death -- but it sounds like this new witness will also aid the investigation.