Russia definitely had the motive.
By why use a nerve agent when they could of just paid a Muslim to cut his throat, and not trace back to Russia?
Why leave a plausible, if not probable link back to Russia?
How would that be in their interest?
To send a messy message: After being released from Russian prison Skripal was traveling to countries, including the Baltic States discussing Russian intelligence techniques.
Maybe as a warning to Putin’s other enemies?
Information obtained from the US federal contracts registry reveals that the Pentagons Defense Threat Reduction Agency (DTRA) has funded a number of military projects performed at #PortonDown, over the last decade
https://govtribe.com/contract/idv/hdtra112d0003