A knife-wielding lunatic allegedly stabbed a man in the back at a Manhattan subway station for accidentally bumping into him on the staircase — only to be freed without bail Tuesday.

Raymond Kwok, 27, savagely knifed his 29-year-old male victim shortly before 9 p.m. Sept. 20 at the entrance to the L train at 14th Street and First Avenue in the East Village, cops said.

The victim was trying to walk down the stairs to the station when he accidentally bumped into Kwok and the pair started bickering, authorities said.

Kwok then stabbed the victim in the back with a knife and fled, cops said.

The victim was transported to Bellevue Hospital in stable condition to receive stitches from the attack, which was captured on surveillance video.

Kwok, who lives in the East Village, was arrested Sept. 23 at the same subway station. Manhattan prosecutors revealed at his arraignment Tuesday that cops found three knives inside his pockets, including a switchblade.

He was charged with assault in the second degree, attempted assault and criminal possession of a weapon.

Prosecutors were seeking to hold Kwok on $25,000 cash bail, but Manhattan Criminal Court Judge Michael Gaffey decided to cut him loose on supervised release despite the charges being bail-eligible.

Kwok is due back in court Oct. 31.