Lynch's lawyer, however, questioned a direct link in Wednesday's arrest, three days after Lynch played in the Pro Bowl.
"When we make an arrest, we believe it to be justified," Culver City Police Lt. Dean Williams told ESPN.com on Tuesday.
The case has been turned over to the Los Angeles County District Attorney, who is expected to formally charge Lynch for possession of a loaded weapon by the end of the week.
In response to media inquiries, the Culver City Police Department on Sunday issued a brief statement that Lynch was arrested for possession of a concealed firearm, but Williams said the actual charge was for possession of a loaded weapon. The gun was an unregistered 9 mm.
The NFL and the Bills, meanwhile, are withholding comment.
Gun safety is a significant issue in the NFL. It has been a hot topic since New York Giants receiver Plaxico Burress was arrested on two felony charges in December after accidentally shooting himself at a Manhattan nightclub.
NFL commissioner Roger Goodell has taken a low-tolerance approach to repeat offenders, and although Lynch never has been suspended, he has gotten into trouble repeatedly. Lynch will turn 23 in April.
"We may not wait for the legal process to conclude when we have repeat offenders," Goodell said Jan. 30 at his annual state of the league address before the Super Bowl. "You can have a false accusation once, maybe twice. When you start getting into multiple accusations, you are putting yourself in the wrong position. You are making the wrong decision. You are in the wrong places.
"At that point in time, you are reflecting poorly on the NFL, yourself, your teammates. That does damage for all of us."
Sunday's police-issued statement noted officers spotted three men in a 2006 Mercedes-Benz and recognized Lynch as the Bills' running back. Williams added Tuesday the car "was stopped for minor traffic violations, and as I read the report they were well-justified."
The statement said the gun was determined to be Lynch's. Williams declined to provide details how the officers reached their conclusion. He also declined to say whether Lynch was driving the Mercedes or where the gun was found.
"I don't believe he thinks Marshawn was driving the vehicle, and I don't believe he thinks the gun was found on Marshawn's person," said Lynch's attorney, M. Gerald Schwartzbach. "The car was not stopped for any kind of driving violation. It isn't a situation that involved violence or the threat of violence."
Schwartzbach conceded he hadn't yet reviewed a copy of the arrest report.
The Los Angeles County Sheriff Department's inmate database says Lynch was booked at 7:12 p.m. and was released on a $35,000 bond at 8:45 p.m.
Williams said it's not unusual to see Mercedes-Benzes in Culver City, Calif., home of Sony Pictures (formerly MGM Studios). He noted the patches on their police uniforms read "The heart of TV and Screenland" and that celebrity arrests aren't foreign occurrences there.
Lynch last summer was the subject of a hit-and-run investigation in Buffalo after his luxury SUV struck a woman in the street and sped away.
After nearly a month of posturing from Lynch's lawyers and the Erie County District Attorney, Lynch paid a $100 fine in a plea agreement. He didn't face criminal charges because the woman's injuries weren't serious enough. She received seven stitches at a local hospital.
"He's not someone who tries to get in trouble," Schwartzbach said. "He's not someone who tries to violate the law. He just isn't. I hope that this is going to be resolved as quickly as possible and as fairly as possible.
"I'm hopeful he comes out of this with his career intact."
In 2006, as Lynch was about to enter his junior season at California, he was the target of a drive-by shooting outside his prep alma mater, Oakland Technical. Police determined Lynch was the victim of mistaken identity.
Lynch ran for 1,038 yards and eight touchdowns last season. He also caught 47 passes for 300 yards and a touchdown.
"I've known Marshawn for a few years," Schwartzbach said. "Obviously, I'm his lawyer. I'm his advocate. Completely, aside from that, I think he's a terrific person. As big as his heart is on the field it's just as big off the field, and that's saying an awful lot."
Tim Graham covers the AFC East for ESPN.com.