Justin Bieber's Dad -- Partner In Crime

Justin Bieber's father helped facilitate the insanely stupid moves of his son that landed him in jail ... TMZ has learned.

Sources familiar with the situation tell us ... 38-year-old Jeremy Bieber was not only present when Justin was arrested early Thursday morning ... he was one of the people who helped block off the residential street so his son could drag race.

It's even worse ... Jeremy was in SET nightclub just before the arrest with Justin and was around him all day, when the self-confessed little pothead was smoking weed.

As we reported ... Justin admitted that he was under the influence of Rx drugs, alcohol and weed at the time of his arrest ... and Justin's dad was right there in the mix.

Unbelievable.