Nolan Wells Drowning Theory 'Questionable' to Ben Crump, Says He Knew How to Swim

Attorney Ben Crump says claims Nolan Wells drowned in Mississippi's Gulf Coast are highly suspect ... because Nolan definitely knew how to swim.

The civil rights lawyer who's representing Nolan's family tells TMZ ... Nolan took swimming lessons as a kid, and he'd been to Horn Island before, so he wouldn't have been lost or disoriented.

As you know ... Nolan disappeared during a Fourth of July celebration with friends on Horn Island, and 2 days later, he was found dead in the water off the coast of the island.

While investigators told us they haven't found evidence of a crime yet ... alleged contradictions in the stories told by the three guys Nolan went to the island with, and the girl he supposedly stayed with on Horn Island raised red flags for Crump. So, did a video purportedly capturing Nolan arguing with someone hours before his disappearance.

Crump joined us Thursday on "TMZ Live" ... saying he thinks race might be playing a factor in the investigation, and Nolan's family fears Mississippi officials might try to sweep his death under the rug.

Nolan's parents appeared on "Good Morning America" Friday and told Michael Strahan they're demanding answers in the case ... noting they just want "honesty and transparency."

A GoFundMe set up to support the family has received hundreds of thousands of dollars in donations already ... including from celebs like Lil Rel Howery.