The Tallaght man had been originally charged with threatening to kill the kidnap victim, but these charges were dropped after he pleaded guilty to false imprisonment.
The kidnap happened at the Glin Stores in the north Dublin suburb when shopkeeper Sean Cummins was held hostage in Clondalkin by an armed gang for almost four hours.
Mr Cummins managed to break free and ran into a house on the Woodford Estate, seeking refuge while gardai were alerted.
Hanlon was due to appear before a sentencing hearing at Dublin Circuit Court when he suffered minor leg injuries in a bizarre shooting incident on the evening of November 21, two days before his court date.
No one has ever been arrested in relation to the incident, which led to Hanlon's case being adjourned.
Sources say gardai are working on the theory that he shot himself to avoid going to prison.
A source said: "This fella is capable of pretty much anything."
In the past, Hanlon has been the victim of a pipe bomb attack, a savage assault and was pepper-sprayed in a nightclub incident.
He has numerous previous convictions and has been arrested for offences such as blackmail, extortion, threats to kill, assault and burglary.
He was regularly spotted in the company of terror chief Declan 'Whacker' Duffy before the latter was extradited to the UK to serve a sentence for murdering a British soldier.
'Whacker' Duffy and his associates were involved in a gangland war against 'Fat' Freddie Thompson's drugs mob in 2007 and 2008.