Two of the guys looked at wristwatches, that seems significant. So I'm leaning towards it either being the rough-looking guy (who looked at it), or the man without a coat. The culprit is left-handed since he wrote on his right hand, and people usually wear watches on their non-dominant wrist so they don't get in the way. That guy's wearing it on his right wrist.
That aside: a live-in maid not allowed to have a smart phone at all is just weird. Don't know if it's weak writing to justify the code (though could easily be explained as "they didn't want to leave a direct text trail") or cultural differences in expectations for workers. At bare minimum, that sounds like a pretty controlling employer and unpleasant work environment to me.