There's a beautiful article written in Hebrew on Chadrei Chadarim about Nachman Kletzky, the father of Leiby Kletzky, paying a shiva call to Rav Chaim Kanievsky. When Mr. Kletzky found out about the petirah of Rebbetzin Kanievsky, he made plans to travel to Israel to be menachem aveil. When someone asked what had prompted him to trouble himself to travel so far to console the mourners, he replied that when he was sitting shiva for his son, the Rav and Rebbetzin had sent him an emotional letter consoling him so he felt he had to console the Rav.
Mr. Kletzky related that he had heard stories about faith from people who came to be menachem aveil him a number of months ago.
People decided to strengthen themselves and some took upon themselves the yoke of Torah and mitzvot.
He said that a fifteen-year-old boy had been sentenced to a two year imprisonment. A few days after the murder, the Kletzky family received a letter from the boy who was in prison. In the letter there were four dollar bills. The boy wrote that he received a small daily allowance for food and cigarettes. When he heard about the shocking murder he decided to give up the money and donate it leilui nishmat Leiby. In the merit of Leiby, he decided that he would don tefillin and keep the Sabbath.
May the mourners be comforted betoch shaar aveilei Tzion v'Yerushalayim.