I’d say no-one better tell Grand Designs (TV show) about that strip of land … they’ll have someone build a strange shaped house on that prime piece of real estate!
Seriously though, it does look like it could be a valid escape route for a local who may know about it. If DJK didn’t just run out of the front door, that is. I’m sure the police would have searched it for any weapon, cast-off blood, etc.
(Not personally struggling with Morgan inviting DJK into the flat, sundaymorning123, he was evidently looking for company that night - judging by the calls he made to friends - and JR was out with the girls, and possibly may have thought of staying at her boyfriend's place afterwards and changed her mind.)