 Many members of congress had already departed in advance of the long Memorial Day holiday in the US. BBC News initally reported some witness as saying the sound may have been a car backfiring.
<fluency>  Many members of congress had already departed in advance of the long Memorial Day holiday in the US. BBC News initally reported some witness as saying the sound may have been a car backfiring.
 Many members of congress had already departed in advance of the long Memorial Day holiday in the US. BBC News initially reported some witness as saying the sound may have been a car backfiring.