Krzysztof has been a good friend of the mathematical Italian Community, and more specifically of the Italian groups of research in Riemannian Geometry and Mathematical Physics. The main event gathering Italian mathematicians is usually considered to be the Congress of Unione Matematica Italiana, scheduled every four years. The last Congress took place in Bari, the week September 24-29, 2007. At the opening of the Geometry Session of the Congress, a message communicating Krzysztof's death was read to the audience and a minute of silence observed in his memory. During the last fifteen years Krzysztof had become a regular visitor of some of the main mathematical Italian institutions. The first time I met Krzysztof was in early September 1994, during a meeting gathering mathematicians and physicists and held in Trieste. Krzysztof's name was already well known for his theory of quaternion Kaehler reduction, and at that time Krzysztof was working on some remarkable aspects of that theory in Sasakian Geometry. I had studied his work and it was natural for me to approach him. His first visit to Rome was in 1998 and we started to know each other better. Since then, for about ten years, I had the good fortune to become very close to him and to be a coworker of him in a couple of projects. I consider Krzysztof the best friend I gained in my mature life. He left to me the witness of his generosity, of his simplicity, and of course of his way of doing mathematics.
Krzysztof shared his mathematics with many Italian colleagues and students. He actually taught introductory research courses in Rome, Pisa and Cortona, this last a small town where Krzysztof gave a summer course for graduate students. He was very proud of the work of his Italian student, Daniele Grandini, who defended his Ph. D. thesis in Milan in June 2007. On September 24, 2007 I received a message from Daniele, and then I wrote to the Italian colleagues who had shared with me the friendship with Krzysztof. I report a few words in a couple of reply messages.
Paola Matzeu (colleague in Cagliari, Sardinia, and coworker of Krzysztof) wrote: "This is to me a very sad news. Kris had a non common humanity and generosity, in particular among mathematicians of his level. This made him a really unique person. I have no words."
Max Pontecorvo (colleague in Roma III and student at Stony Brook in the same years of Krzysztof) wrote: "It is with great sorrow that I get this sad reality, that I was already prepared to have to suffer. I had been in apprehension since I was informed of the accident. I knew Kris since the times of the Ph. D., he was a very simple and pleasent person and a was doing a really beautiful mathematics. It was always a great pleasure to take part to his talks when you were inviting him. I can imagine how we will miss him."
In my message I communicated the death of Krzysztof together with another news. His book with Charles Boyer was going to appear shortly in Oxford University Press. It is now in all our libraries and it contains of course the best description of Krzysztof's research interests during his last years. This, together with the work that will be done starting from what Krzysztof did, will help to maintain him among us. A workshop dedicated to his memory and with title "Kaehler and Sasakian Geometry" will be held in Rome in June 2009.