The first police-baton blow to the head easily doubles the suspect over.

But the blows keep coming — two, three, four — sending him crashing to the lobby floor, where he curls up and writhes as the baton falls again and again.

On Day Two of testimony in a police-brutality trial, Manhattan prosecutors yesterday released the first images from a video that caught the 2008 police beating of a suspect at a West 93rd Street housing project.

Housing cop David London — a 15-year NYPD veteran and married father of three kids — had been on patrol when he went to close the front door of the Hostas Houses building, which had been propped open.

He ran into Walter Harvin, a young Army vet who had recently returned from Iraq. Harvin is seen on the tape rushing to enter the building, where his mother lives, before London shuts the door.

Thy begin an encounter that would end with Harvin covered in blood and bruises from more than 20 baton blows and kicks — the final few of which rained down even after London and his partner cuffed the man.

“Everybody in America should see that video,” said Harvin’s mother, Cora Page, 46.

“But I don’t want to see it.”

And she didn’t, remaining in a courthouse hallway as the entire video was played for jurors.

But prosecutors released only snippets to the public yesterday and excluded all portions where Harvin was handcuffed.

The cameras in the housing-project hallway clearly capture the lead-up to the beating. Harvin pushes past the cop to enter the lobby, and the two apparently exchange angry words, although the video has no audio.

“I’ll f- – – you up! I’ll kill you, motherf- – -er!” Harvin shouted, according to London’s partner, Mohammed Khan, who testified yesterday.

At one point, as London prevents Harvin from going in the elevator, Harvin shoves the cop.

“I came from Iraq!” Khan remembered Harvin shouting during the beating.

“I was in the Air Force, too!” the cop answered, still swinging.

Defense lawyers say the missing audio, and the fact that Harvin kept thrashing, even in cuffs and even in the police car, will show that London’s force was necessary.

Prosecutors counter that nothing justifies so many blows.

Still traumatized, Harvin has disappeared, his family said. He is not expected to testify.

laura.italiano@nypost.com

