Security Onion has tools included (specifically Network Miner and Xplico) that can do this.
Is the assignment to only look for 'malicious activity'? As that can be a bit broad if you're not sure what to look for specifically. (example: machine is sending out a lot of spam, malware downloading other files (GET or POST), ....)
Two things that can, in most cases, help what you're looking for is: NetworkMiner & NetworkTotal
Don't rely solely on those though, carve through the PCAP yourself (using Wireshak for example), filter packets which you think are interesting (for example only HTTP traffic) and create a new, smaller capture to be able to spot weird behaviour more easily.