A dog is supposed to be man’s best friend - but instead of protecting his own home, a golden retriever became a partner in crime when he smooched up to a thief stealing from the pet’s family home.

Last month in San Diego, a thief entered a property with an open garage around 10.40pm.

The alleged thief saw a number of bikes and picked one to take off on. But he paused once he saw the golden retriever approach him.

It looked like the thief had second thoughts on stealing the bike, and started to walk this getaway transport back into the garage.

In a bizarre turn of events, surveillance footage from the home caught the man telling the dog he was the coolest and a sweetheart before he called out for the retriever’s owner.

“Where’s your dad, your dad shouldn’t leave the garage open,” the suspect said. “Dad, where are you?”

Man's best friend turned partner in crime when a bike thief in the US strolled into an open garage and came across the home owner's affectionate golden retriever. Photo / CBS8

Police said it was a rare sight.

“The subject comes in, grabs the bike, starts to walk out, the dog comes out the side door he comes back in and starts playing with the dog for about a minute…. Heads back out,” San Diego Police Department Lieutenant Bryan Brecht said.

 “Very unusual. I haven’t seen anything like that in my career.”

The man then picked up the $1300 bike and rode away, but not before he told the dog he loves him.

The dog is then very briefly seen following the thief before stopping at the garage entrance.

“He’s a nice dog, very friendly. Again, like you said he doesn’t look like a guard dog,” Brecht said.