11:35 AM PT -- Nashville PD has released the latest evidence they have of Riley Strain being seen on the night in question -- and it comes courtesy of none other than bodycam footage from a police officer.

In the body cam video -- which was rolling while the officer was checking out a burglary call on a vehicle -- you can see Officer Reginald Young interact with Riley who casually strolls right by him ... they even exchange a brief hello, and RS looks fairly normal and put together.

Nashville PD says this appears to be the last sighting of him on camera before he vanished.

A major clue has been uncovered in the disappearance of Riley Strain ... as authorities discovered the missing college student's bank card Sunday near a river in town.

According to Nashville Police, Riley's bank card was found on the embankment between Gay St. and the Cumberland River -- where surveillance video is said to have last captured Riley. No other update was issued ... except that the search for Riley continues.

This update comes after Nashville's Office of Emergency Management had the dive team search for Riley in the Cumberland River on Saturday. As the OEM put it to FOX17 ... the search plan included taking several boats along the riverfront where Riley was last seen.

Based on indicators from search K9s onboard, sonars were used to locate areas where divers could look more thoroughly. Saturday's search reportedly resulted in no conclusive findings. Additionally ... the outlet says police do not currently suspect foul play.

However, a local eyewitness claimed to FOX17 Riley was not alone after leaving Luke's 32 Bridge Friday evening. A homeless man detailed that he and his wife, who live by the riverbank, heard a commotion and allegedly saw Riley almost stumble into the river.

He added ... "I never seen anybody stumble that hard before," while claiming RS looked very intoxicated.

The man claims he didn't explore the situation further, claiming someone was apparently already there with Riley, who assured him Riley was just drunk. No word on who that person might've been, or any description of them. The FOX17 report didn't elaborate either.

Remember ... the Tennessee Alcoholic Beverage Commission is currently investigating whether Riley was overserved at Luke Bryan's Nashville bar. While the establishment is cooperating with authorities, they defended themselves in a recent statement that they only served Riley one alcoholic drink (and two waters) before asking him to leave.

The country superstar himself also spoke out on Riley's disappearance, calling the whole thing scary and asking for prayers.

For anyone who may have reliable information on Riley's whereabouts, cops encourage you to call 615-742-7463.