Why did Russia keep him locked up for 13 years than release him...just to poison him later? He was a double agent, I’m sure no one would care if Russia just killed him when he was locked up.
Putin wasn't President in 2010 when the spy trade happened, it was Medvedev.
The Brits insisted on Skripal being part of the trade for him and 3 other Russian nationals for 10 Russian spies captured in the US.
Medvedev gave him a pardon too.