There is indeed a correlation between the two. Crime has plunged while pot laws have loosened. There are now 23 states and DC with medical mj laws. It does not necessarily mean there is causality, but there is definitely a strong correlation.
...but a clear relationship between the lax attitudes on crime that began in the 1960s and the more strict measures that started being implemented in the 1990s when people were concerned over high crime rates.
The strict attitudes on crime, especially drug crimes, began in the early 1980s. It wasn't until the 1990s that drug laws began to loosen. The correlation is weaker. Other correlations are present as well, including strengthening of gun rights and widespread use of the internet. I suspect those have contributed, as well.
The bottom line is that the drug warriors who screamed about rampant crime have been proven wrong. Loose marijuana laws have not led to an increase in crime.
Once again, you are attributing a causative effect to a correlation where no causative mechanism exists.
The drug laws were strict since the early 1900s, and crime was low until the permissive attitudes of the 1960s became widespread. In the 1960s, prison sentences were reduced because very vocal activists started blaming everyone but the criminal for crimes committed, and pushed strongly for lenient sentencing and alternatives to prison, like attendance at group therapy. This is also the time when crime started to explode. In the 1990s, as a result of widespread criminal behavior, people started pushing back against the anti-prison activists. They voted for 3 strikes laws and minimum prison sentences for crimes were enacted.
I should also point out that in the 1960s, one could go to prison in CA for possession of marijuana. That changed sometime in the late 1960s/early 1970s, so that by the end of the 1970s, possession of less than a gram of marijuana was a misdemeanor, not a felony. If more lenient marijuana laws can really cause a drop in criminal behavior, then why did crime rates keep going up after marijuana laws were “liberalized” in the 1970s?
To attribute the drop in crime to legalization of marijuana is to completely ignore the proactive anti-crime laws that were enacted at the time.