I often hear writers say that there reaches a point when the story writes itself. The idea being that once all of the groundwork has been laid, the events that follow are natural and logical, based on the circumstances. It may mean smooth sailing for the writer. It also means a boring journey for the reader.
This is a point I often struggle with because I am a concise writer. I want to get to the point and move on. For essays and short stories, it's wonderful. For trying to keep the reader guessing or maintaining suspense, it's lousy. This is where extraneous information comes in.
Throw the audience for a loop. Tell them stuff that isn't actually relevant, but sounds like it might be. When a murderer is on the loose, have the neighbor show up because she was feeling friendly. Is she creating an alibi? Is she looking for her next victim? Is she simply a lonely woman looking to kill an afternoon? We won't know until the next thing happens. But you do know. You know she has no purpose but to throw us off the trail of the real killer, who we met in the first chapter.
If the only person you mentioned aside from the main characters was the gardener, the gardener would be mighty suspicious. But by throwing in four ancillary characters, it looks like you are just building mood and ensemble. It allows you to hide the real points in plain sight. Then when you reveal it, we all get so surprised to find out, so annoyed that we didn't figure it out, but also satisfied because of that.
When you use extra information to keep the audience interested, you are not using more words than you need. So you can still be concise and confusing. Give it a shot.