The FBI has replaced Osama Bin Laden with an accused child pornographer on its Ten Most Wanted list of fugitives. How does America's most prominent federal law enforcement bureau choose who is featured on the list?

Bin Laden was one of the world's most wanted terrorists before his death in a May US special forces raid in Pakistan. Eric Justin Toth, 30, is not accused of killing anyone, but of producing child pornography.

The former school teacher and camp counsellor has been on the run since 2008, when he was indicted on federal charges in the state of Maryland after child pornography was found on a camera he had used at a school, officials say.

The FBI has followed him through Illinois, Indiana and out west to Arizona, but the trail ran cold.

The answer Top ten most wanted fugitives must have a federal warrant out for their arrest

They must be considered dangerous - "a menace to society" in bureau parlance - and worthy of a $100,000 reward

Other leads must have run dry, with agents deeming the publicity might help find the fugitive rather than drive him or her further underground

So on Tuesday, the bureau added Mr Toth to its Ten Most Wanted list, replacing the al-Qaeda leader who was killed by US forces last year.

"We have always counted on the public's support to help capture fugitives and solve cases," Mike Kortan, a bureau spokesman, said in a statement.

"The addition of Eric Toth to the Top Ten list illustrates how important it is to get this individual off the streets and into custody."

The FBI first drew up a Ten Most Wanted list in 1950 when a reporter asked the bureau for the names and descriptions of the "toughest guys" on the run.

Since then, the list has proven a remarkably successful publicity programme, FBI officials say.

WHO, WHAT, WHY? A part of BBC News Magazine, Who, What, Why? aims to answer questions behind the headlines

Of 495 men and women on the list since then, 465 have been captured or located. Of those, 153 were nabbed after a tip from the public, the FBI says.

The ten individuals on the list are not ranked.

To be included on the list, a fugitive must have a federal warrant for his or her arrest and must be a real menace to society - someone with the capacity to do continued harm if he or she remains on the run. He or she must also be bad enough to warrant a $100,000 (£62,900) reward.

Who else is on the list? Jason Derek Brown: Accused of killing an armoured car guard during a robbery in Arizona

Accused of killing an armoured car guard during a robbery in Arizona Joe Lui s Saenz: Accused of killing two rival Los Angeles gangsters, raping and murdering his girlfriend, and killing a fourth person

Accused of killing two rival Los Angeles gangsters, raping and murdering his girlfriend, and killing a fourth person Glen Stewart Godwin: Murdered a fellow inmate in a Mexican prison, then escaped

Murdered a fellow inmate in a Mexican prison, then escaped Robert William Fisher: Accused of killing his wife and children

Accused of killing his wife and children Semion Mogilevich: Wanted for allegedly defrauding investors in a stock scam

Wanted for allegedly defrauding investors in a stock scam Eduardo Ravelo: Accused member of a drug gang

Accused member of a drug gang Alexis Flores: Accused of kidnapping and murdering a five-year-old girl

Accused of kidnapping and murdering a five-year-old girl Victor Manuel Gerena: Sought in connection with the robbery of $7m from a security company

Sought in connection with the robbery of $7m from a security company James "Whitey" Bulger: Accused Boston gangster and murderer; captured in June FBI Ten Most Wanted

The case agents searching for the fugitive will have exhausted other leads and believe the publicity will help find him or her. (In cases that don't make the list, agents may feel they are closing in on the bad guy and the publicity will drive him further underground.)

The FBI adds fugitives to the list by canvassing its field offices for suggestions, analysing the most worthy cases, then forwarding those up the bureau's chain of command until they receive final approval from Director Robert Mueller.

"Over time, the top 10 list has in some ways mirrored the criminal investigative interests of the bureau and the priorities of the day," says John Fox, the bureau's official historian.

In the 1960s and 1970s, violent anti-Vietnam War radicals like Bernardine Dohrn, Katherine Power, and Leo Burt featured on the list, for example.

In the 1990s, international terrorists made the list, and since 2000, several alleged child pornographers and paedophiles have been listed.

"Of course, it doesn't capture all of what the FBI's priorities are," Mr Fox says.

UK's most wanted The UK does not have a Most Wanted individual or top 10 list

Crimestoppers' Most Wanted website is the closest equivalent

Since 2005, the site has hosted more than 7,459 appeals

Approximately 20% have resulted in an arrest by a call to Crimestoppers

Low-quality photos and a reliance on police to report arrests lower the success rate

Police choose appeals for the site - these are organised by crime type and location Source: Crimestoppers

"Counter-intelligence is not an investigative matter that is well suited to the Top Ten Most Wanted list."

Fugitives are removed from the list when they are captured, die (or are killed) or are removed because they are no longer considered a menace to society.

Over the years, six fugitives fell into that category; several of those were anti-Vietnam War activists accused of violent acts who evaded the law until they reached middle age.

The bureaucratic process of adding a new fugitive to the list can be lengthy.

The FBI took 11 months to replace Bin Laden. As of Wednesday, Bulger was still on the list, though he was captured in June.

Reporting by Daniel Nasaw in Washington