Saint Louis is getting to be a more and more dangerous place to be.  Police say they have made three arrests after a night of violence that saw six homicides in the city in a 12-hour span.  Police Chief Sam Dotson and Mayor Francis Slay discussed the crime spree at a Thursday afternoon news conference.  They did not identify the suspects in custody, who will be formally charged on Friday.  The killings include the fatal shooting of a 50-year old hotel manager shot in the head during an early Thursday robbery attempt at a Drury Inn near Interstate 44 in south Saint Louis.  No arrests have been made in that case.  Police say the three arrests were made in shootings that involved domestic issues where the victims knew their killers.  Another killing involved a robbery that was likely drug-related.