I just can't figure out this leaving the back door unlocked Angelo. Anyone could have walked in while JeM was away. Are we sure he didn't unlock it?
Anyone could have been upstairs waiting for him to return. Who knows? Perhaps someone was, and snuck out while the CL's back was turned.
I find the lock/unlock/key/no key situation completely...odd and improbable.
I also find Mr. Harrod's car parked on one specific side of the driveway odd. Seems like if you only had one vehicle you'd just pull in center, unless you were expecting another vehicle(s). I wonder when Mr. Harrod last operated his vehicle- and if it was operated by anyone else after he disappeared?