The US has stupid extradition treaties with various countries. Basically, they refuse to let any of their own citizens be extradited, but get extremely pissy if any country refuses to deport one of its own citizens.
It's a nightmare for British citizens because it's very difficult to get out of it, and US sentences are often draconian compared with those in the UK.
In 2002 an Autistic British man was caught hacking into the US military and NASA servers, bringing down a Washington office and a US Naval base for 24 hours. He was looking for evidence of alien encounters. He has been fighting extradition ever since and, if convicted, faces 70 YEARS in prison. Bearing in mind the longest hacking sentence handed down in the UK is 2 years and only 23 people have ever received whole life sentences for anything in modern times.
He's facing the same sentence as particularly heinous serial killers like the Wests or the Moors Murderers did in the UK