<human>: Could you distill the essence of the text into 1-3 sentences?

I'm not even sure if this should be a part of this subreddit, but I'm honestly stumped about the repeated theft occurring in my club.

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I've been making budgets and handling money from my school club, as we're a student-run group. We've had a theft happen before, partly my fault for misplacing an envelop containing ~$400 in an unsafe cabinet, so this was notified to the executives, but not reported immediately.

A few months later, another theft occurred, about another $500 or so that was taken directly from the cashbox. What made me suspect it was an inside job, was that the note containing how much payment was received was left, and I did not even notice the money was missing for an entire week despite keeping the cashbox in the office. The two incidents were reported about a month after the 2nd incident occurred, and not much action happened with the campus security (it was not reported to the police).

The office is shared by 2 other clubs, but the cashbox was placed inside the locker (password for locker is only for the club executives) since the two thefts. Cashbox was kept in the cabinet (which was also locked, but easy to pick into) before the 2 incidents.
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About a week ago, our club had a major event, inviting about 150 people. When I calculated the ticket cost ($30 per person), we should've had $4500 in the cashbox, but when I deposited the cash (immediately after the event), I only had $4100. There were about 3 people who watched an received payment other than myself, and I'm more than convinced that someone has been consistently stealing from the cashbox. All three have been around when the other 2 incidents have occurred.

I'm honestly stumped about what I should do. Do I report it to the police? Do I just try to talk it out with the club? This is a $1300 loss from the club in total now, and I just have no idea to go from here.
<bot>: multiple theft in a student-run club, most likely by a fellow executive. $1300 has been stolen over the year, stumped on what I should do at this point in time.