I don't think it was that suspicious. Tessio's men had been removed from the hospital only about 10-15 minutes prior to when Michael arrived. Another important point to consider: it was 1945 - there were no cell phones (how wonderful, but I digress!). According to McCluskie, he "thought I had all you guinea hoods locked up." So Tessio's men were taken straight to jail. So if Michael arrived shortly thereafter, then it is highly likely that no one had the time, nor the opportunity, to call.