After TMZ published pictures of Justin Bieber** smoking what appears to be marijuana on Dec. 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."

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.

"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."

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."

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 Usmagazine.com: Justin Bieber's Team "Isn't Happy" About Marijuana Pictures Leaking Online