As the SEPTA subway train rocked forward, a thirty-something guy leaned over near the doorway and gently planted a kiss on the little boy at his side.

When the train neared the Fairmount Avenue stop shortly after midnight on Thursday, the man reached out like an adoring parent and directed the 3- or 4-year-old tyke to an open seat.

Then he flew into a monstrous rage.

Without uttering a word, police said, the unidentified man whipped out a double-claw hammer and began bludgeoning a 20-year-old man who was dozing off in his seat.

For five long minutes, SEPTA surveillance cameras captured the deranged attacker - who was still on the loose late last night- digging his hammer into the man's head and neck.

Through it all, disgusted investigators said, at least 10 passengers stood by and did nothing as the random attack moved from the train to the platform, when the hammer-wielding maniac tried to push his victim down onto the train tracks.

When the beating was finished and the suspect fled with the little boy, the victim staggered back onto the train, bloodied, confused and alone, said Detective Kenneth Roach, of Central Detectives.

And even then, no one tried to help him.

"Somebody should have helped this guy," Roach said. "I understand the [other] guy had a hammer, but they outnumbered him at least 10 to one."

Miraculously, the victim took the subway up to Temple University Hospital, received several staples and sutures and was discharged, Roach said.

The motive remains a mystery.

"I'm baffled," Roach said. "He had no reason to do that. It was unprovoked. The victim was just going home from work, minding his own business, listening to his iPod."

Roach said that the victim, whose name was not released, boarded the subway at City Hall.

The attacker - a bearded, stocky, 5-foot-9-inch black man who wore a yellow shirt and black pants - also got on at City Hall, with a youngster who may or may not be his child.

The victim and the hammer-toting psychopath never exchanged a word or a glance, Roach said.

"According to the victim, there was no contact or verbal discussion," he said. "They didn't even notice each other."

The hammer was hidden in a black-and-yellow book bag that the attacker clutched throughout the short subway ride.

The little boy dashed off the train with the other passengers during the brutal beat-down, but was later seen running back on to recover the book bag. The boy and the suspect are seen on camera leaving together.

Roach described the attacker as "very dangerous" and asked anyone who knows him to contact police at 215-686-3093 or -3094. *