R. Jay Soward -- I'm Devastated By Cousin's Prison Murder

Former NFL receiver R. Jay Soward -- a 1st round pick in 2000 -- says his entire family is "traumatized" over the prison murder of his cousin ... who cops suspect was killed by ex-NFL star Lawrence Phillips.

As we previously reported, R. Jay's 1st cousin Damion Soward was murdered last week while serving time at Kern Valley State Prison ... and cops say Phillips, his cellmate, is the main suspect.

"It's very, very traumatic for my family," Soward says.

"I have no words ... I have no words for what happened to my cousin."

"We were tight. Very tight. I just want to find out what happened. That's the only thing I care about."

Soward -- who spent 4 seasons in the NFL -- tells us he never crossed paths with Phillips during his time in the league ... "didn't know him, never spoke with him."