Complex sentence: After a 16-hour standoff, during which areas of the Sydney central business district surrounding the site were cordoned off and nearby buildings were locked down, police officers from the State Protection Group stormed the café.
Split into simpler sentences: After a 16-hour standoff with the police, during which areas of the Sydney central business district surrounding the site were cordoned off and nearby buildings were locked down. The crisis ended as police officers from the State Protection Group stormed the café.