However, the passenger - the target of the officer's gun - maintained he had simply been reaching for papers on the floor to try to find the vehicle's license and registration, as requested.
A video, apparently recorded by a woman in the car, begins as the male passenger is expressing incredulity that the officer has pulled a gun.
"Wow," the passenger says in the video, laughing. "We're looking for the f-ing paperwork, bro. Oh my God."
"I understand that," the officer replies. "Don't move, all right?"
The passenger sounds indignant as his hands remain on his lap. "Why are you still pointing that gun at me, bro?" he asks the officer. "Why are you still pointing the gun at me, though? Record this sh*t. Why are you still pointing the gun at me, bro? My hands are right here."
"I understand," the officer says.
"No, you don't understand," the passenger protests, as the officer tells him to relax. "No, I'm not going to relax. Get the f***ing gun off me."
A woman in the car asks the officer: "Is that really necessary? His hands are both out."
The officer says it is necessary as he waits for backup to arrive, eliciting another round of protests from the vehicle's passengers. For several more minutes, they remain at an impasse, and the passenger mutters periodic complaints as music plays in the background. The entire time, the officer's gun is trained on the man.
Towards the end, the officer says something through the radio and the passenger begins protesting again. At one point in the video, the officer mentions that there had been a screwdriver on the floor of the car.
"Why are you trying to make this bigger than it is, bro?" the passenger says. "We complied with everything you asked for."
The video lasts a little more than nine minutes total, and the officer's gun is pointed at the male passenger the entire time. Police said the officer had to wait longer than usual for backup to arrive "and provide assistance in safely resolving the situation".
"We understand that it is never a comfortable position to have a gun pointed at you, regardless of whether it is a police officer," police said. "Unfortunately, the length of time that the officer's gun was drawn lasted much longer than normal based on his location."
Police said the traffic stop was resolved amicably.
"In the end, the officer had a conversation with the passenger of the vehicle explaining his actions and why the gun was pointed at him," police said. "The passenger indicated he understood why it happened and actually apologised to the officer. Both the driver and the passenger were issued citations and were allowed to leave."
However, the video was uploaded to Facebook last Saturday with a caption that suggested there may not have been as much understanding as police thought. (Note: The video contains profanity.)
"CAMPBELL COP IS A B--!!!!!!!!!!" wrote a Facebook user named "Feo Mas" who identified himself as the passenger in the video. "(He) pulled out a gun cuz I reached for paperwork he asked for."
A week later, the video had amassed nearly two million views on Facebook, as well as tens of thousands more on YouTube. Online, a debate raged: Several people defended the police officer and said they felt the passenger should have remained quiet, while others were outraged at how long the officer had trained his gun on the passenger despite the man's hands being visible at all times.
Police departments are under increased scrutiny for violent, often fatal interactions with suspects. So far this year, 594 people have been shot and killed by police, according to the Washington Post's Fatal Force database. Last year, police shot and killed 963 people.
The Facebook user who posted the video did not respond to an interview request sent by Facebook Sunday.
The Campbell Police Department said it was aware of the video circulating online, as well as the thousands of comments surrounding it. Police also cited an officer-involved shooting that had taken place in nearby Los Banos, California, as an example of the "unfortunate reality" that people sometimes attack police.
"As an agency, we can understand the response to the Facebook video, and that is why we have and will continue engaging our community," police said. "The comments on the Facebook video bring up a lot of different viewpoints about how the officer could have responded differently or used different tactics. Our officers receive a tremendous amount of training on a consistent basis and that training is what dictates our response. This is intended to protect our officers as well as those they come in contact with."
Police said they had reviewed footage from the officer's body cam, which included the beginning and end of the traffic stop, not shown in the Facebook video. The department did not release any footage from the officer's camera and did not immediately respond to an email Sunday.
"We are thankful that this resolved itself with no one getting injured and hope that this additional information provides clarification," police said.