Its a tragedy.
H5N1 avian flu emerged in china in 2003. As of May 2020, the WHO reported a total of 861 confirmed human cases which resulted in the deaths of 455 people. It was observed that cases occurred in people handling birds. There was no human to human transmission. But the possibility that a mutant form could arise that led to this transmission was real and scary. There would have been a pandemic.
In 2011 Ron Fouchier of the Erasmus medical center in Rotterdam presented work where he created a pandemic virus. H5N1 was passed through ferrets, an ‘animal passage’ experiment. He would infect one ferret with the virus, wait until it got sick, and then remove a sample of the virus that had replicated in the ferret’s body. As the virus multiplies in the body, it mutates slightly, so the virus that came out of the ferret was slightly different from the one that went in. He would take the virus from the first ferret and infect a second, then take the mutated virus from the second ferret and infect a third, and so on.
After passing the virus through 10 ferrets, Fouchier noticed that a ferret in an adjacent cage became ill, even though the two hadn’t come into contact. That showed that the virus was transmissible by air in ferrets and, by implication, in humans (Ferrets have similar lung physiology to humans). The pandemic virus was created and sat on his lab shelf. It is probably in his freezer today. Virus sequences produced by this accelerated evolution method cannot be differentiated from ones arising naturally.
This is an example if a gain of function experiment. A wild virus is modified to see if it could become a pandemic pathogen in humans.
The future beckoned, brave scientists would examine dangerous viruses for pandemic potential in their labs. A jump start on creating a vaccine for the virus would be enabled before the virus had become pandemic capable. A compelling idea?
Since then researchers have created a menagerie of pandemic viruses in their labs using both direct manipulation of virus genomes, animal pass through and combinations.
These PPPs (potential pandemic pathogens) are the most dangerous substances humans have created. More dangerous than radioactive materials, and lethal toxins. An escape could mean hundreds of millions of people dying.
Fouchier’s lab was only BSL (biological safety level) 2 (they run from 1 to 4 with level 4 the most secure). Also, The Erasmus medical center is in the middle of the city of Rotterdam, providing a petri dish of closely packed humans for the virus to replicate in if it escaped.
From Oct 2014 to Dec 2017 there was a moratorium on gain of function experiments. Scientists argued about the benefits versus the risks of this type of research. In the end the proponents of this research won and gain of function experiments resumed. Many scientists disagree .
There have been many cases of escapes of dangerous diseases from labs . Just looking at SARS escapes (particularly dangerous since there is no cure)
The SARS outbreak of 2002–2003 eventually spread to 29 countries, causing over 8,000 infections and at least 774 deaths. There have been six separate escapes from virology labs studying it: one each in Singapore and Taiwan, and in four distinct events at the same laboratory in Beijing.
The first escape was in Singapore in August 2003, in a virology graduate student at the National University of Singapore. Fortunately he got treatment and recovered without the virus spreading.
The second escape was in Taiwan in December 2003, when a SARS research scientist fell ill on a return airflight after attending a medical meeting in Singapore. He remained at home for 5 days, unwilling to seek medical care because he dreaded bringing disgrace to himself and his institution. He was only persuaded to enter the hospital when his father threatened to commit suicide. Investigation implicated exposure due to an attempt to decontaminate a bag of leaking biological waste, perhaps without proper protection and against protocol. Fortunately, the disease didn’t spread.
The other four escapes were all at the Chinese National Institute of Virology in Beijing. A total of nine cases were identified involving researchers and their families. A parent of one researcher died.
Evidence for each case
- Location of outbreak, near china’s only BSL-4 lab containing the worlds largest collection of bat coronaviruses. Experiments manipulating viruses and animal pass through to make them more infectious take place here. There are thousands of wet markets in China.
- The virus has not been found in any animal samples from the market.
- The closest known virus sequence is from a sample held at the lab taken from a bat in a cave in Yunnan.
- The bat caves of Yunnan are 1000 miles away. Bats cannot fly that far.
- Bats have never been on sale at Wuhan seafood market. In any case these are tiny insectivorous bats which are not generally eaten. Asian bat eating is mostly confined to large fruit bats.
- There could have been illegal sales of banned species at the market, such as pangolins. These illegal animals are trafficked by a vast network of criminal gangs from all over the world to China. Would the outbreak have occurred at just one wet market if this was the source?
- Minks are highly susceptible to the virus. They are also closely related to ferrets, a popular lab animal for pass through experiments. The particular features of covid19 can be generated by these experiments 
- Lab escapes are not rare events (see above).
- Past pandemics have been caused by species jumping in the past. It is clearly not impossible
- A nature paper  says that it can’t be from a lab because “no one would have thought to make that sequence” but if the virus was created by accelerated evolution using animal pass through then it would look just like a naturally occurring virus. It is a weak argument
So the bits of evidence for the lab escape hypothesis stack up, for natural emergence not so much. However, we will probably never know for sure.
There is no reason to suspect intentional release. China got unlucky. This escape could have been from a western lab.
Is China to blame? No. In the realm of cutting edge research China is still more a follower than pioneer. The construction, and operation of the lab would have followed western practice. i.e. an entirely inappropriate level of security for the creation of dangerous potential pandemic pathogens.
In an extraordinarily prescient paper in 2012  the authors calculate that, with the number of operating labs performing experiments that generate PPPs, pandemics caused by lab leaks will be more frequent than those caused by natural spillover.
They propose a new type of lab (BSL4+) that would be appropriate for this type of research.
- Located in a remote region far from human habitation.
- Full time technical staff would perform the experiments, communicating with principal investigators via video link.
- On site accommodation provided, staff would undergo a period of quarantine before being allowed to leave the site after their shift
They propose a small number of such labs to serve the world. Pandemic pathogen creation to be banned in all other labs.
What happen next?
Whether covid19 came from the lab or wild it makes no difference to the pandemic response. We have to vaccinate everyone.
But it does make a difference to future research.
If you are 100% convinced by the spillover theory then you will be arguing for the creation of more labs of the current type so that scientists can take more samples from wild animals and perform more gain of function experiments.
But if you think covid19 might be a lab escape then this means closing down current dangerous operations, building the BSL4+ labs and banning these experiments in all other labs.
With the circumstantial evidence pointing to a lab escape it is up to proponents of the spillover theory to provide hard evidence for their theory.
China wants to build 5 to 7 more BSL4 labs. Others probably have plans too.
Instead, lets build a small number of BSL4+ superlabs as an international collaborative project.
In the meantime. Leave those wild animals alone!