> Making it possible to contract a murder

Paying criminals was possible before cash was invented, and it will continue to be possible into the future. We even have movies that have hitmen being paid in gold, diamonds, favors, and other exchangeable assets as major plot devices.

> difficult to achieve

Our ancestors successfully exchanged goods and debt thousands of years ago. I doubt modern humans will have any difficulty inventing new non-cash methods of paying for services.

This isn't theoretical, because we already see soap and other easy to fence goods used as exchangeable assets.

https://priceonomics.com/why-thieves-steal-soap/

    Products like cigarettes and soap are appealing because they can
    perform some of the major functions of money. Since there is a
    consistent demand and market for them [...] they retain their value.
    [...] Since they have standard sizes, they can also be used as a
    unit of account. [...]
    
    In areas where fences or other buyers are always willing to purchase
    stolen products, soap is just as good as money.

This concern about the anonymity of cash is propaganda. While everyone is concerned that a few poor or middle class people might get away with laundering petty amounts of money, the real thieves move far larger amounts of non-cash, very trackable money to corrupt politicians and offshore havens.