Lawyers for Freddie Mac’s former president and chief operating officer said the recently fired executive plans to “provide valuable assistance” to federal investigators looking into accounting problems at the GSE. Attorney Thomas Vartanian said David Glenn, who was terminated for cause in June, acted properly while overseeing questionable derivatives transactions between 2000 and 2002. Glenn agreed last week to pay a civil penalty of $125,000 to the Office of Federal Housing Enterprise Oversight, and