Complex sentence: Harris gives a copy of the tape recording to Jessner, but British security forces kidnap and kill Harris, and blame his assassination upon the IRA; without Harris to authenticate it, the tape recording can be dismissed as a forgery.
Split into simpler sentences: Harris gives a copy of the tape recording to Jessner, but British security forces kidnap and kill Harris, and blame his assassination upon the IRA. Without Harris to authenticate it, the tape recording can be dismissed as a forgery.