After TMZ published pictures of Justin Bieber smoking what appears to be marijuana on Jan. 4, the 18-year-old singer apologized to his young fan base via Twitter the following day.

Though Bieber is taking the high road by owning up to his indiscretion, behind the scenes, a source tells Us Weekly, his team "isn't happy about those photos. They are grilling security about who could have taken them."

PHOTOS: Celebrity pot smokers

Bieber's BFF, 19-year-old rapper Lil Twist, is believed to have been partying in the hotel room, too.

The pictures were reportedly taken on Jan. 2 inside a hotel room in Newport Beach, Calif. Just one day earlier, a paparazzo was killed while trying to photograph the singer's Ferrari in L.A. Though Bieber was not in the vehicle at the time, he expressed his condolences in a statement to Us.

PHOTOS: Celebrities with Bieber fever

"While I was not present nor directly involved with this tragic accident," the Canadian crooner said, "my thoughts and prayers are with the family of the victim."

VIDEO: Justin Bieber models for Us Weekly!

In the June 2012 issue of GQ, Bieber's manager, Scooter Braun, said the "Beauty and the Beat" singer goes to great lengths to maintain a squeaky clean image. "He knows that I hold him to a high standard," Braun said. "He doesn't want to blow it."

PHOTOS: Inside Justin Bieber's workout routine

That wasn't the only reason Bieber wanted to steer clear of trouble. "For me, it's just like, I like to be in control of myself. I mean, I've had a beer, like, before. . . But I never get out of control," the pop star told the magazine. "I mean, I keep my guard up a lot, because you know, you can't trust anyone in this business. That's what's sad. You can't trust anybody. I learned the hard way."

This article originally appeared on Justin Bieber's Team "Isn't Happy" About Marijuana Pictures Leaking Online