WASHINGTON (AFP) - Shamed US financier Bernie Madoff, serving a 150-year prison sentence, is back in the spotlight as the star of an exhibit in a US museum dedicated to gangsters and serial killers.

A baseball bat engraved with the former mogul's name, a letter in which he seeks forgiveness from his son Andrew and even keys to his old New York office are on display at Washington's National Museum of Crime & Punishment.

In total, some 15 items that once belonged to the famous fraudster or are in some way linked to him, are on view.

The 75-year-old, who once chaired the Nasdaq stock exchange, was found guilty of being behind a massive Ponzi scheme.

He took in billions from thousands of clients over decades, building a reputation as a shrewd investment manager by paying out fake "profits" to some investors by plundering the new cash from others.

But his pyramid fraud collapsed in 2008, wiping out numerous family fortunes. He was arrested in December that year, and pleaded guilty in 2009.

"The general public thinks of crime as a violent crime, but there are many that are not violent, we make sure that in our museum we focus on everything," Janine Vaccarello, the museum's chief operating officer, told AFP.

She said the items were given to the museum by Madoff's son, liquidator Irving Picard or even victims.

The Madoff display case is placed next to a wall dedicated to Frank Abagnale, a con artist made famous by the film Catch Me If You Can starring Leonardo DiCaprio.

Vaccarello said Madoff is "by far the largest financial criminal, with thousands of victims and in many countries. He is considered the worst of the worst."

"If it looks too good to be true, it can't be true and don't invest your money," summed up Joe Persichini, the retired assistant director in charge of the FBI's Washington Field Office, at the exhibit's opening.