Prowler
/ˈpraʊlər/
Definition 1 of 2
Pro Tip 1/3Negative Connotation
The word 'prowler' often implies a threat or danger when describing a person. 
The neighborhood watch alerted everyone to the presence of a prowler.
Pro Tip 2/3Stealthy Movement
'Prowler' indicates moving quietly and with caution to avoid being seen. 
The security camera captured a prowler sneaking around the backyard.
Pro Tip 3/3Criminal Activity
A 'prowler' is often associated with illegal activities like burglary or trespassing. 
Residents reported a prowler looking through windows late at night.