I'm saddened to hear this. Karl was a longtime Chicago Critical Mass rider and a great guy. I'm glad I got to ride with him during the April Mass. If you still need help getting in touch with people who knew him, please contact me at jgreenfield[at]streetsblog.org. Here's a quote from Karl from the 20th anniversary celebration for the Daley Plaza rides:
Karl Szwet, an HVAC technician from Highland, Indiana, who’s been riding with the Mass for many years, told me a story about the early days, when participants posted flyers in Spanish in Pilsen days before the ride to alert residents that the ride would be coming their way for the first time. “So when the Critical Mass did go through the neighborhood, everybody was out. Every porch had people on it waving and clapping, and all the lights were on. It was so exciting to see it — it was like we had bridged something there.”
A couple of pieces of info that may be useful for tracking down Karl's truck:
Here's our memorial to Karl on Streetsblog. https://chi.streetsblog.org/2018/06/04/cycling-through-heaven-on-th...
Memorial ride for Karl this Friday 6/29 6pm from Daley Plaza. "Shortly after May's Critical Mass ride, longtime CCM participant Karl Szwet suffered a heart attack and passed away some days later in a hospital. Karl started riding in Critical Mass in 1999 and hundreds of people knew him through his tireless enthusiasm and advocacy over the years. He may have hailed from Indiana, but Karl was a true Super Fan of everything Chicago, especially Da Bears! This month's Critical Mass ride is dedicated to Karl, biking by some of his favorite South-side spots, and then ending for a tribute at Soldier's Field." https://facebook.com/events/869483309896419/