Very weird behaviour from flatmates

As the title says, I have experienced some very weird behaviour from some people/person in my flat. I need some help if anyone knows how to make it stop / identify the culprit. For reference I live in a flat of 10 people (including myself) made up of 6 girls and 4 boys, with half domestic and half international students. Everyone is a second year except for 1 girl (referred to as N), several of the students are muslim however no one eats halal food and no one else has any dietary requirements so no one has been able to be ruled in or out based on what has been stolen

The odd behaviour began in September when we all moved into the flat for the first time. No one had met each other before other than 2 of the girls who had lived in the same flat the year prior and HATE each other (lets call them B and L) and me and another lad who had met at a party last year and somewhat got on (at first). The initial behaviour was simple stuff like stealing food and washing up liquid and other basic behaviour which is sadly to be expected, towards the end of September there were a few arguments going on in the flat at the time, The two girls previously mentioned and me and the other boy previously mentioned regarding his drug usage (smoking a lot of weed in the bedroom next to mine) when the behaviour moved from plain theft to active tampering of food and electrical equipment, things such as a pasta I had food prepped having a strong smelling powder poured into it (still not sure what but we came to the general consensus of chilli powder or something similar) and the ketal having honey poured into it. The week both these incidents happened was followed by a large amount of arguing between everyone as the first thing we all did was just start blaming each other which ended with the accommodation reception being involved.

The reception sent out a group email essentially telling us all to stop arguing and didnt really acknowledge the root cause of the thefts/tampering's . The tampering's subsided briefly but picked back up in October when a girls (who had been the predominant victim of a significant amount of the food thefts - but not the tampering's - She will henceforth be referred to as N) fork kept getting moved into peoples cupboards, we believe this was in an attempt to start the group arguing off again however this didnt happen as the second person whose cupboard the fork was placed in (my own) was home for a weekend so was ruled out immediately and it was realised that whoever was moving it was just trying to cause arguments. Again this culminated with an email from reception asking people to not touch each others things.

After this the food thefts increased again to the point where for 2 weeks straight nearly a pint of milk was being stolen daily. This is the point where we realised that whoever was doing it was not short of money but was actively seeking to be malicious. Again we spoke to reception but nothing was really done other than the threat of a 'all flat meeting' - something which nearly everyone wanted and pushed for but reception wouldn't do.

In November things got more serious when a knife which was gifted to me from a restaurant I worked for prior to uni was stolen (something which has still not been returned) and was extremely valuable. This caused a massive amount of arguments between me and the other lad previously mentioned as I believed he had stolen and sold it for drug money, this almost ended in a fist fight on several occasions however his girlfriend (who he had met at a party in September) is a childhood friend of mine so managed to make us chill out before things got too bad. After this ended I began believing that it was either this boy or another girl - lets call her B. B has lied to us all year in a kind of Jay Cartright from the inbetweeners style - basic things like popularity, grades and weirdly her age (claiming she was 21 and in third year - actually proven to be 19 upon seeing her ID at a nightclub and her being in my 2nd year friends classes who are also on her course). Upon hearing about this the reception took a bit more interest this time and had individual meetings with everyone and conducted room searches, the knife was not found. Little information was gathered in these meetings as the receptionist conducting them was also a student at the uni (not sure which year) who had lived in the accommodation the year prior so was well aware of the drama between B and L. Instead of doing her job she decided to ask us all about the drama in the flat rather than about the knife with a predominant focus on B and her ex. This receptionist was also sleeping with the best friend of the lad I had been arguing with at the time. This receptionist left the staffing team in December, im not sure as to why. After this whole incident me and this lad became more or less mates again and just put it behind us (we still have the odd argument but nothing like we used too). Nothing was found in the room searches other than a little bit of weed, which he got in a small amount of trouble for (just a warning)

From this point on things were getting stolen more and more all the way until the Christmas break with N being the target again. Over the Christmas break almost everyone went home, except for L and an indian international student who was on a nursing placement at the time. Nothing was reported to have happened over christmas until B came back early and started arguing with L however this is pretty common.

For the first week in Jan everything was quite chill until peoples stuff started getting moved around and stolen again. This caused reception to have a generalised flat meeting with us which they didnt tell us about. They just kind of walked into the flat and knocked on peoples doors, unfortunately they decided to do this has 7pm on a Wednesday leading to only 4 people actually being in at the time. Following this meeting things started getting stolen at an alarming rate. At this point I broke up with my long time gf (unrelated reasons and she didnt live in the flat) and began to spend alot more time with N, we had grown close when her bf cheated on her and I was pretty upset so I spent alot of time with her. 5 days after this, N's room was broken into whilst we were at uni and her room was ransacked - nothing seemed to be missing but things were pulled out everywhere and her hairbrush and mug were smashed. We called the police who didnt show up (welcome to England lol) and just gave a CRN and the uni police didnt really care either. This is the second time the police had been called that week as L and B had gotten into a physical fight the night before (again the police did nothing)

That is all the major details and im wondering like what do we do at this point, reception and police dont care and they refuse to allow us to install any kind of recording equipment for fear of breaching GDPR