Is the person stealing, or keeping a secret stash? There's a big difference. The difference might not be obvious as both types of behaviors prevent access to materials. But there is a difference, especially in the context of a lab.
For example, in wet labs, there's a system of stock solutions vs. working solutions. The stock solution is kept on a separate area where everybody has access to it, and there is an expectation that everybody be extra careful not to contaminate or mishandle the container (e.g. leave it outside if it belongs in the fridge, expose it to light, etc.) Problems arise when the lab does not have a good system of restocking the stock solutions, or where not everybody is careful regarding cross-contamination and handling issues. In these cases, people tend to keep a secret stash of stock solution, just to make sure they have access to materials when it's time to do particular experiments. Everybody keeping a secret stash brings about a host of new problems, like added costs, solutions expiring, and more. But the problem is not that lab personnel are being evil and "stealing" the stock solution, but bad lab management.
So from your comment,
We found out that our coworker was hiding materials and even throwing them away when they realised they might get caught.
This sounds like keeping a stash, and then panicking when caught and trying to get rid of the evidence, perhaps because keeping a stash is not allowed by lab rules, while the underlying issues have not being fixed. And according to comments by the OP, the discarded materials were a few uL in an otherwise used tube. And $500-$1,000 worth of materials can fit in a 50uL microcentrifuge tube, so the amount itself is not surprising. Before going too far with the accusation, I'd make sure others are not doing the same thing.
You also need to be careful with how you present your accusations. Even if the OP has other information that would make this actual "stealing", getting caught stealing is quite an embarrassing situation, which can spill into overwhelming feelings of shame. In a lab situation, where people work together with shared resources for years at a time, it can make the perp feel overwhelmed (e.g. "everyone knows I'm a thief and treats me like one"), which can end up in serious stuff, like suicide. This is not a far-fetched idea, and it's the reason we professors, when catching a student cheating, we are careful to refer to the student as "someone who was caught cheating" as opposed to "a cheater." The first describes a reversible situation (the student can accept the consequences and stop cheating), the second describes the character, the being, of the person and is a judgement on that person.
Whatever the facts, you have to tell someone up the chain of command of the incident. Even if the lab is well managed and what this person did is inexcusable, everyone deserves a second chance. But it's not your job to administer discipline in the lab, it's your supervisor's job. They have to decide if this is an isolated incident. And if it's the first time, it needs to be put on file so that the second time counts as the second time. If it's the second, third, or fourth time, then the supervisor needs to know so that they can refer the student to the next person up the chain. It also gives a chance to the supervisor to learn about the possible underlying problems, like issues with keeping enough stock materials for everyone to do their experiments.