A timed delay between blasts is a tactic historically associated with “secondary device” terrorist attacks meant to target first responders – Google Search https://www.google.com/search?q=A+timed+delay+between+blasts+is+a+tactic+historically+associated+with+%22secondary+device%22+terrorist+attacks+meant+to+target+first+responders&newwindow=1&sca_esv=f299872650e10ca8&rlz=1C1ONGR_enUS1133US1133&aep=1&cs=0&hl=en-US&prmd=ivns&sxsrf=ANbL-n5lPqF5ZbO3wxCT0AX45SGcWSdqtw%3A1779549979143&source=lnms&fbs=ADc_l-aN0CWEZBOHjofHoaMMDiKp0UJuhqwKhR0QUhF54-6jIf5FTMC_zgepHBqt1YxkrDc7UKkeLkqmlgcJTOaXASt8tVTtBknVz0Y-86qpnBNBhpadlWMc1M-x6SliegnhtwmA91S8SSPCAAuvYNWWB8Jum61Y92eIfz2L9rFumC-BA0ciSUabgV9HZeotVf0uc3C15