The ex-daughter-in-law of fugitive Eddie Maher said she told US authorities about his true identity because she "feared for her life".
Maher - known as "Fast Eddie" - was jailed for five years at Southwark Crown Court on Tuesday for the 1993 theft of a security van holding £1.2m.
The 57-year-old spent almost 20 years on the run in the US before being arrested in February last year.
Jessica King said she felt "threatened" and "it was the right thing to do".
Maher, from Essex, had been wanted by police since the Securicor van he was driving disappeared from outside Lloyds Bank in Felixstowe, Suffolk, on 22 January 1993.
He used false identities while on the run and built a new life in the US, but was arrested in Missouri last year.
The court heard Maher's life unravelled when his son's disgruntled ex-wife Jessica contacted US authorities to tell them he was a wanted man.
Earlier she told ITV's Daybreak she was not motivated by the £100,000 reward offered by Securicor for Maher's capture and return of the money.
Ms King said: "I was in fear for my life and to be honest it was just the right thing to do.
"When Eddie found out I knew, he threatened my life, so really it had to be done."
She said she had no regrets about her decision, but if a reward was forthcoming it would be "very welcome".
"That is in the hands of my lawyer. The money would extremely help, raising a child by yourself is very difficult," she added.
During Tuesday's hearing, David Nathan QC, mitigating, said Maher's former daughter-in-law had originally been the partner of his son Lee's best friend.
He said Lee won a lot of money on the lottery and she left her partner to marry Lee.
He added, when the money ran out, she researched the name Maher on Google and found out his true identity.
Mr Nathan said she heard there was a reward and went to police.
Maher, originally from South Woodham Ferrers, was due to stand trial for theft after being deported, but changed his plea to guilty.
The court heard he gained £200,000 from the theft.
Police and prosecutors are now preparing to retrieve Maher's fire service pension pot - thought to be about £125,000 - through court proceedings.