San Francisco police said cellphone thieves are getting more sophisticated and now they have video from a Muni bus to prove it.

Investigators said they're hoping someone recognizes the thieves.

Police said three men tried to steal a woman's cellphone on a Muni bus.

The video shows the thieves, a young man in the white T-shirt and a second person in blue, standing by the door.

As the bus came to a stop, the man in white reaches for the woman's cellphone with both hands and headed to the exit which was held open by the suspect in blue.

Police said a third suspect in black, behind the victim, may have been there to keep any good Samaritans from getting involved.

In this case, the victim held on, even as she was dragged out of the bus.

Police said she never lost her grip on the phone and got back on the bus unharmed, but they're troubled by what they saw.

"It's not just one person, (it's) three individuals working together and if they can do it on one bus, they may be able to do it on several others," said San Francisco police Officer Carlos Manfredi.

San Francisco police said this attempted robbery happened on the 33 line at 18th and Church streets in the Castro last month.

Police are now asking  people to be on the lookout for similar suspicious activity on public transportation.

As smartphone thefts continue to become more common, police said the best bet is to keep hold of phones when approaching a stop.

Police have described the first suspect as an African American man, 5 feet 5 inches tall, 140 lbs, and was last seen wearing white T-shirt, blue jeans and a backpack.  The second suspect is an African American man 5 feet 8 inches tall, weighing 150 lbs. and was last seen wearing all black clothing. The third suspect is an African American man 5 feet 11 inches tall, wighing 150 lbs. and he was last seen wearing blue sweatshirt.