New York CNN  —  Three weeks after the murder of UnitedHealthcare CEO Brian Thompson, companies and executives are closely monitoring threats from customers and shoring up their security vulnerabilities. A Texas man was arrested Friday for allegedly threatening Capital One executives over email, in which he expressed frustration over a disputed debt. Taylor Bullard, 34, claimed he had already paid $543 he owed and lashed out at the bank for its persistent efforts to collect the sum, according