Former CEO of Zurich Insurance Group AG Martin Senn, who left the company in December, has killed himself, marking the second suicide among the insurer’s top management ranks in the past few years. Mr. Senn’s death at age 59 follows the suicide of former Zurich Insurance Chief Financial Officer Pierre Wauthier in 2013. An internal probe at the insurer, conducted under the supervision of Switzerland’s financial regulator, later cleared company leaders of placing an inappropriate amount of stress on Mr. Wauthier. Mr. Senn stepped aside in early December 2015, capping what had been a difficult period for the company. At the time, Mr. Senn cited Zurich Insurance’s difficulties in revamping its largest business, and its failure to seal an ambitious acquisition of U.K.-based RSA Insurance Group PLC. Mr. Senn, a former executive at Credit Suisse Group AG, joined Zurich Insurance as chief investment officer in 2006 and later assumed the CEO role in 2010.