Why would my case be consider inconclusive when I had video footage of a suspect. The cop did a poor job with investigating

My car was keyed by a tenants boyfriend and we had video footage of him being the only one that walked by my car within 24 hrs and you could tell hy his hand movements he did it. The cop who investigates our case did nothing till we filed a complaint that he wasn't doing anything. The cop didn't even interview the suspect till 2 weeks after the keying and did it by phone. The case took a long time and was told due to inconclusive evidence I couldn't even get a police report for my insurance company. I'm convinced being the cop didn't want to deal with the case this guy got away with everything and cost me money.