heavy security, around around airports and metro stations as a matter of routine. but what we've seen here today is clear demonstration once again. if you're a determined suicide bomber, or a bomber of another society, it's virtually impossible to stop that person from detonating explosiveses in a crowded, public area. ali? >> all right. matthew, thank you very much. i'll let you go and proceed to gather more information for us. we'll check in with you later as we update this story. our senior national correspondent. well, look, their jobs have always been risky but it has been a particularly dangerous 24 hours for police across the country, at least ten law enforcement officers have been shot in the last 24 hours. the latest incident began early this morning in st. petersburg,