A career criminal who promised to knock out the first white man he saw has been jailed for 25 years after throwing a punch that killed a 62-year-old man.

Lashawn Marten, 44, went on a racist rampage in New York back in September 2013 when he started randomly attacking innocent bystanders around Union Square.

When he punched retired train engineer Jeffrey Babbitt, knocking him out, the impact of his head hitting the pavement killed him.

Lashawn Marten is seen at his sentencing in State Supreme Court on September 12, 2017 in New York

In the same brutal day of violence, he punched a 19-year-old pedestrian and later Matthew Cortellesi, 50, who had tried to help Babbitt.

Marten stood over the dying 62-year-old who had blood pouring from the back of his head bragging about his attack.

When Cortellesi tried to step in, he got sucker-punched which knocked him out cold for seven minutes, breaking his rib and causing nerve damage to his face.

Marten, being sentenced in Manhattan on Tuesday, offered an emotionless apology to the family of the man he had killed before being sent to jail until he is almost 70.

He said: 'I would like to just apologize to Mr Babbitt's family and friends and to the other two I hit. I'm sorry.'

Lashawn Marten, 44, went on a racist rampage in New York back in September 2013 when he started randomly attacking innocent bystanders around Union Square

Justice Melissa Jackson handed him the stiff sentence after his attorney had sought a 15-year stretch.

Jackson said: 'You intended and you targeted people because of the color of their skin. There's no doubt about it.'

The killer's lawyer Michael Croce argued he was not in control of his actions due to his schizophrenia diagnosis, but the judge dismissed the claims, saying he had an 'abundance of resources' available to him for a decade, according to the New York Daily News.

The attorney said his client had stopped taking his medication and said: 'What benefit is it to warehouse him for the rest of his life, to send him to prison for the rest of his life?'

Marten, an ex-con, had pleaded guilty to manslaughter, assault and attempted assault as hate crimes.