An Irish bank robber, who has been described as one of the most prolific in recent US history, has been sentenced to a further six years in federal prison for a series of heists over a few months in one California city.

Adam Lynch, 37 and from Dublin, is already serving more than five years for other robberies he committed in Colorado and Wyoming.

Tagged the 'Ho Hum Bandit' for his nonchalant, almost bored demeanor as he passed notes to bank tellers demanding sums of cash, he admitted to 17 robberies in the space of just 13 months.

But law enforcement agencies have identified other heists believed to have been carried out by Lynch, with the total running into the mid-20s.

He was arrested after confessing to his girlfriend over drinks in the Fado pub in downtown Denver. She then discreetly left the bar to alert the police.

On Monday in federal court in San Diego, he was sentenced to 70 months in prison, just short of six years.

The judge ordered that 56 of those months be served consecutively with the sentence handed down by a Denver court following his arrest in April 2011.

He will not be released from jail until 2020, after which he is likely to be deported back to Ireland.

The Irish Examiner notes that his arrest ended a spree of robberies that began in California in February 2010 and continued in Colorado and elsewhere into March 2011.

Lynch's defense lawyer, Ronald Gainor, who also represented the Irish man in court in Denver, had argued he should serve no more time than already imposed by the Colorado court.

Gainor said his client had been "an extremely productive individual," who had previously ran a successful dog care business in northern California and lived in an $800,000 home with his, now estranged, wife.

But he said his life went off the rails and he fell into a deep depression following the collapse of his marriage and a battle with cancer.

However, Judge Roger Benitez disagreed and imposed a sentence in line with what prosecutors were seeking.

Lynch had pleaded guilty to seven robberies in San Diego carried out by "force, violence and intimidation," though he was never armed and simply passed a note claiming he had a gun and demanding the money. He was even described as being quite polite during his heists.

In total, he stole some $25,000 from the seven banks in San Diego.

Investigators said he was extravagant with his money, taking his then girlfriend Julia Lundstrom on an exotic round-the-world vacation that included stops in Egypt and Ireland. The couple moved to Colorado, where Lynch continued robbing.

The relationship soured and in April 2011 he confessed to his partner that he was the 'Ho Hum Bandit,' after which Lundstrom called the police and Lynch was quickly arrested.

Lynch pleaded guilty to four robberies, three in Colorado and one in Wyoming, but agreed to pay restitution to six other banks.

In court documents he also said he knew his ex-girlfriend would inform authorities.

Here’s a Fox News report from his initial spree, two years ago: