One possible theme could be obsession. Since it's about a collector, there might be an excessive focus on obtaining certain items, which is often seen in real - life collectors. Another theme could be the value of the items collected. Whether it's monetary, sentimental or historical value, this could be a central aspect.
Themes in 'The Collector based on a true story' might include the search for identity. The act of collecting can sometimes be a way for people to define themselves. For instance, collecting art from a certain era might show a connection to that period's culture. Also, there could be a theme of preservation. If the collector is gathering items with historical significance, they may be trying to preserve a part of the past, much like real - life collectors who contribute to heritage preservation.