I tracked down my son's online bully and called his mother

This kid was someone my teenager had never met in real life. He was a friend of a friend of a friend online. ugh. Exactly the stupid online behaviour I had hoped they would avoid.
So, the teenager in my life got a few pretty toxic online messages. I'm generally fine with banter, sarcastic humour, and other such comments. But this was different.
This was a bit more vicious and involved threats like 'I'll come to your house and stab your dad in the neck and burn your house with your brothers and sisters inside and I'll kill your mum'.
This kid was someone my teenager hadn't met in real life. He was a friend of a friend of a friend online.
Ugh. Exactly the stupid online behaviour I had hoped my kid would avoid.
But anyway, it was a long lockdown and a lot more of teens' lives moved online and we allowed a bit of freedom and this is where we ended up.
We maintained a ban on devices in bedrooms and we reserve the right to know all passwords and we scan chats and conversations and search history on a fairly regular basis, so we didn't just hand over the keys to the kingdom or anything.
The kid's name was on his Snapchat.
This kid mentioned his school in his chat and linked out to a sports team. He also mentions his home area in the actual targeted abuse.
A quick google showed that the team does indeed play at the school which is in the area in his bio.
Let's call him Dudley — because the only Dudley I know is young Dudley Dursley who's so horrible to Harry Potter.
Anyway, this Dudley has a real-life surname with a pretty unusual spelling variation. An online search links to his Instagram where he has a photograph.
Then I googled people of that name in the county he mentions. Sure enough, up pop mum and dad on Facebook. They even have a range of photos of this kid on their timelines — and these photos are of the kid with the insta account. Their significant family occasions and occupations are listed. His siblings are named and there are plenty of pics of them too.
I now know where Dudley's dad worked for the last few years and when he was away from home for work. I can see where the Dursleys shop, what sports they enjoy and where they've gone on holidays and when their wedding anniversary is.
This all takes around three minutes and no particular 'private investigator' style skills — it's all there on mum and dad's Facebook accounts.
I look at the messages again and wonder if I'm the bad one here.

Actually, re-reading: "Ur a ugly little handicap and when I catch u I'll put u ina wheelchair" and "ur a freak, handicap" and "u won't be able to leave ur house cause it will be burnt down and ur family will be in it. I'll slit ur mothers neck off and stab ur da 3 times in the head" helps me make up my mind.
This is unacceptable behaviour if it a 13/14 year old and it is outright terrifying if it is actually an adult pretending to be a child.
I message the mum and ask her to call me. She does. I explain that I am aware that teenagers do 'stooopid stuff' and may not realise that something they just throw out there may have a bigger impact than intended.
I keep it friendly. I just want this mum to monitor her son more carefully from now on. My teen will have learned that online information can be used in all sorts of ways and that online behaviour can 'come home' pretty quickly and easily. And we'll all move on.
Nope. She is adamant that her Dudley would never bully anyone. She actually says "we are a non-bullying household". As if other households proudly declare themselves pro-bullying or something.
She said that her darling son's phone was probably hacked. She mentions 'the Russians' who do that sort of thing.
She says it's impossible for her child to mention disabilities in such a negative way as there is disability in their own extended family.
Maybe I'm wrongly blaming this teenager. I feel a bit guilty.
She confirms they do live in the town mentioned in one of the threats and that her son is the age he mentioned online and that he is on the social media groups used.
She says she's not very tech-savvy so she wouldn't be able to look at his history or retrieve deleted or sent messages. She again speculates that it was probably hackers. I ask her to talk to her son anyway and she agrees.
She calls back to say it couldn't be her son who burst into tears the moment she mentioned the threats.
He also told her that somebody else was using his phone the previous day.
I point out that the messages were sent the day before that again.
He now remembers that it was actually that day that he noticed his phone seemed to have been 'hacked'.
He had not told her about this possible hacking at the time.
I point out it is unlikely that hackers of any nationality would infiltrate a teen's phone to send messages to another teen. Just threats — no demands for money or bitcoin or nudes or anything.

I also ask her why these foreign hackers would specifically mention their home area in one of the threats.
She says these hackers can find out anything about anyone. For a woman who claims to be not very technical, she sure knows a lot about the capabilities of these pesky hackers.
I send her pics of the threats. She sends me one of those emails you get when you log back into an account. The one that asks if it is 'really you'.
She includes the IP address the most recent log in was for. She does not know if she would be able to check her own IP address as it's "locked to private" and she's not very tech savvy.
I google the IP address. It says it's linked to the town in which she lives.
I ask her to chat to her son again and to come back to me. She hasn't bothered yet.
In my mind, I am pretty satisfied that her son did send those messages. It is slightly reassuring that this teen is in school and unlikely to come to my home. It is slightly terrifying that this teen has outsmarted his 'handler' and that the only lesson he is likely to have learned is that threats and cyberbullying are easy to get away with.