City firms must ask more questions about the origin of some of their foreign clients' funds, the former employer of a Russian lawyer who died in detention in 2009 said last week.

Jamison Firestone, managing partner at London legal consultancy FD Advisory, worked with Sergei Magnitsky, who died in a pre-trial detention in 2009 after accusing Russian police of complicity in a $230m (£140m) tax fraud. Magnitsky's posthumous conviction for tax evasion caused international outrage last year.