"in what" in a news post body

A post body from TikTok:

Terrifying CCTV has captured a failed assassination attempt on a man with his young daughter in Sydney's south‑west, in what police allege is linked to the city's underworld.

I can't understand the function of both "in" and "what" here.

My thought:

1. The attempt is "linked to the city's underworld."
2. Police allege the attempt is "linked to the city's underworld."
3. Is it right to introduce a non-restrictive relative clause with "what" rather than "which"? I never saw this before.

This is typical newspeak for reporting on crime.

What happens in an incident is alleged to be x, y or z by the police.

They write "in what" because until the case goes to trial and a verdict is reached, it's an "in what is alleged". The press cannot state that it is in fact linked to organized crime. "what" here is an object, not a relative pronoun (which).

So, the grammar is: The cops allege the attempt on the man's life is linked to the city's underworld. attempt there is a direct object.

To refer to that, we use: "in what police allege is linked to organized crime." " Other examples

Alexander Soofer, the executive director of the Los Angeles housing organization Abundant Blessings, has been charged with multiple counts of fraud and embezzlement in what is alleged to involve $23 million in contracts. Nonprofittimes

World cycling's governing body, the International Cycling Union (UCI), will not give an immediate response to claims made by the United States Anti-Doping Agency (Usada) over its role in what is alleged to be "one of the most sordid chapters in sports history", but has promised not to "delay matters any longer than necessary".
The Guardian