Jon Venables served eight years in prison for the torture and murder of the toddler in the northwest English city of Liverpool, before being released with a new identity in 2001.
He pleaded guilty on Wednesday to four counts at a hearing at England's Old Bailey central criminal court in London.
Venables admitted to having 392 category A images -- the most extreme -- 148 category B and 630 category C images, and to having a "paedophile manual".
Bulger's father Ralph and mother Denise Fergus were in court to hear the guilty plea.
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Bulger's mother Denise Fergus earlier said that the latest crimes proved "beyond any doubt what a vile, perverted psychopath he has always been."
In a case that shocked the country, Venables and his friend Robert Thompson, who was also 10 years old at the time, abducted Bulger from a shopping centre.
The little boy's mutilated body was found two days later on a nearby railway line.
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