The suspected gunman who killed 3 people and left 5 injured after he shot up a waterfront bar and restaurant in North Carolina Saturday night appears to have scoped the site out the night before the attack … and there’s video evidence.

Check out the clip … an eyewitness tells TMZ the accused killer Nigel Edge can be seen floating about 20 yards away from the American Fish Company in Southport, located on the Cape Fear River.

A person — apparently Edge — is behind the wheel of a white center console motorboat with the phrase “Game On” emblazoned on the side. The whole vessel is dark aside from the navigational lights on the bow. Something spooks him … and he ducks down and slowly heads out of the area.

Southport Police Chief Todd Coring said Sunday the attack was without a doubt premeditated, and prosecutors confirmed in court Monday he was seen floating near the establishment with his lights off Friday night.

And, as we reported, Edge returned Saturday night and wreaked havoc on unsuspecting bar patrons. He was later apprehended by police as he backed his trailer into the water to retrieve his boat.

Authorities say he used a 300 Blackout Sig Sauer rifle outfitted with a suppressor and scope to carry out his slaughter … and also had a .380 handgun on him when he was arrested.

He has yet to enter a plea and is being held without bond due to his being a flight risk and a danger to the community, per the judge presiding over his case. He is due in court on Oct. 13 for a probable cause hearing.

Edge is a former Marine who — as we told you over the weekend — once attended the CMT Music Awards with Kellie Pickler … and sued her earlier this year for allegedly trying to poison him at the event.

He also sued a hospital for medical malpractice … and for allegedly trying to off him as well.

Edge suffered near-fatal injuries while on deployment in Iraq back in 2006 … and says he suffers from post-traumatic stress disorder.