One of the common methods used by money launderers to hide the origin and destination of illicit funds is to create complex corporate structures that obscure the identity of the real owners or controllers of the assets.
Lawyers can facilitate this process by providing legal services such as setting up shell companies, trusts, foundations, or other entities in jurisdictions with weak AML regulations or high secrecy. By doing so, lawyers can help their clients evade taxes, avoid sanctions, conceal criminal activities, or launder money. This is why lawyers are considered high-risk professionals for AML purposes and are subject to due diligence and reporting obligations.
References: = Some of the references that support this answer are:
ACAMS Study Guide for the CAMS Certification Examination, Chapter 3, Section 3.2.2, page 77:
"Lawyers are often used to create complex corporate structures that can be used to hide the beneficial ownership of assets." Money Laundering Reporting Officer: The Role Of MLRO, Section "Money Laundering Risks For Lawyers": "Lawyers are at risk of being used by criminals to launder money through various means, such as creating corporate entities, conducting transactions, or providing advice." New York Lawyer Pleads Guilty to Ponzi Scheme, Money Laundering, Section "Lawyer agrees to forfeit $19 million from investment scheme": "A New York lawyer admitted Monday to money laundering and orchestrating an $18.8 million Ponzi scheme using his Forest Hills-based law firms, Wisnicki & Associates LLP and Wisnicki Neuhauser LLP."

The Basel Committee on Banking Supervision (BCBS) is a global standard-setting body for the prudential regulation of banks. It does not have any formal authority to enforce its standards, but relies on its members' commitment and peer pressure to implement them. The BCBS's principles on customer due diligence (CDD) are part of its guidelines on anti-money laundering and combating the financing of terrorism (AML/CFT), which aim to enhance the soundness and integrity of banking systems. The BCBS's principles on CDD provide guidance to banks and bank supervisors on the essential elements of a CDD programme, such as customer acceptance, identification, verification, risk assessment, monitoring, and record-keeping. The BCBS's principles on CDD are not legally binding, but are intended to be a benchmark for national practices and for banks to design their own policies and procedures. The BCBS's principles on CDD are consistent with the recommendations of the Financial Action Task Force (FATF), the global standard-setter for AML/CFT.
References:
Customer due diligence for banks 1, BCBS, October 2001.
The Basel Committee on Banking Supervision report on customer due diligence 2, Journal of Banking Regulation, 2002.

A money laundering investigation that involves multiple countries can be challenging due to different legal systems, languages, cultures, and levels of cooperation. Two factors that can assist such an investigation are:
Law enforcement and other authorities should have access to financial information that is pertinent to the investigation. This can help them trace the flow of illicit funds, identify the perpetrators and beneficiaries, and gather evidence for prosecution. Financial information can be obtained from various sources, such as financial institutions, financial intelligence units, regulators, and international organizations.
Law enforcement and other authorities should be allowed to establish and utilize joint investigative teams with law enforcement in other countries. This can enhance coordination, communication, and information sharing among the authorities involved, and allow them to pool resources, expertise, and evidence. Joint investigative teams can also facilitate mutual legal assistance and extradition requests.
References:
Financial Action Task Force (FATF), International Standards on Combating Money Laundering and the Financing of Terrorism & Proliferation, The FATF Recommendations, February 2012, updated June
2019, Recommendation 40, pp. 120-123
FATF, Best Practices on Establishing and Operating a Joint Investigative Team, June 2020, pp. 5-6 FATF, Money Laundering and Terrorist Financing Investigations, June 2018, pp. 11-12