This is tragic and shocking news. I visited the Pro Aves yellow-eared parrot reserve at Ventanas in 2019 with Guillermo Nagy to check out their hummingbird feeders, not sure if it was Gonzalo who let us in the gate or one of the other staff. We saw lots of yellow-eared parrots, including a flock of >50 on the Riosucio side of the pass, so it really has been a conservation success story.
Agree Jardin seemed like a safe and welcoming little town, felt fine wandering round on my own and birding from the suspension bridge at the edge of town. I guess it might be a different matter if you are trying to achieve something for nature conservation which is perceived to interfere with someone's criminal economic interests.
It would be good to know if anyone in Colombia is setting up a crowdfunder for his family, or indeed for other conservation biologists killed by criminal gangs.