Police say pain motive in stair slay

The suspect accused of pulling an immigrant woman to her death down a Manhattan subway staircase was trying to hurt her son, who he thought threw trash at him, prosecutors say.

David Robinson, 53, faces manslaughter charges in the shocking July 17 attack.

He allegedly ambushed Than Htwe, 58, (top) and her son Kyaw Zaw Hein, 22, as they were leaving the Canal St. Q train station in Chinatown, yanking Hein down the staircase by his backpack, police allege. Hein reached for his mother as he fell backward and she tumbled down the stairs with him.

“Why did he do it?” the son asked the Daily News after the attack. “We’re not his enemy.”

The son was accompanying his mother to a doctor’s appointment when they were attacked.

Though the assault was initially described as a botched robbery, Robinson (inset) told detectives after his arrest Wednesday that anger motivated him, not greed.

He said he was in the subway station at Canal St. and Broadway when Hein and his mother walked by him and became enraged after thinking Hein threw garbage at him, according to a criminal complaint.

So he followed them to the stairs and pulled Hein by the backpack to hurt him, the complaint alleges.

He saw Htwe fall and heard the crack as her head hit the ground, the complaint says.

Htwe fell into a coma and died 11 days later at Bellevue Hospital.

Robinson was taken into custody following more than four months on the run after a tipster spotted him in Central Park and called police. Cops had identified him as the suspect and released his photo July 28.

He was arraigned in Manhattan Criminal Court on Saturday and remains held on $100,000 bail. While cops initially charged him with murder and manslaughter, the Brooklyn district attorney is only pursuing manslaughter charges against him.