Complex sentence: Upon arrival, the officers allegedly heard gunshots, which created panic and caused party-goers to flee and became engaged in an "unknown altercation with a vehicle backing down the street towards the officers in an aggressive manner".
Split into simpler sentences: Upon arrival, the officers allegedly heard gunshots, which created panic and caused party-goers to flee. Police originally stated there was an "unknown altercation with a vehicle backing down the street towards the officers in an aggressive manner".