After a week of tedious method ical probing, police yesterday re ported no progress toward salv ing the mysterious blast which rocked the Y. W. C. A. and killed the custodian. . Chief of Police Frank Riddle said yesterday that his depart ment has not yet received an FBI analysis report of what type explosive set off the deadly charge. “And we haven't determined a motive,” Chief Riddle added. Carl Ross, 63-year-old janitor at the downtown “Y'* was killed instantly Sept. 19, about five min utes after reporting for work at 7 o’clock. Police have not determined whether the “bomb,” or whatever it was, was intended for Ross or one of the 53 occupants of the building at the time. ,,, Without revealing details of the investigation, Chief Riddle did say that two friends of ten ants of the “¥” told conflicting stories concerning their activities at the time of the blast. While these stories continue to be checked, other investigation teams are compiling volumes of reports on explosive sales, fam ily background of the victim, activities of the tenants and their friends and alleged “grudge” suspects. eeeee,