British Prime Minister Theresa May said Tuesday there must be a "major national investigation" into the use of potentially flammable cladding fitted to high-rise towers across the country, as police formally identified a five-year-old boy as one of youngest victims of London's Grenfell Tower fire tragedy. May's comments came as tests show that all samples of building materials submitted so far — coming from 95 buildings around England — have failed fire safety standards. The national testing was ordered after flammable cladding was blamed for the rapid spread of the June 14 inferno at west London's Grenfell Tower, which claimed at least 79 lives.