Again, the contractors were reimbursed by Livent through false invoices.
Nigeria contends that Mr. Abacha systematically embezzled money from the country's central bank through a system of false invoices.
The authorities said the brothers directed their subcontractors to create nearly $1 million worth of false invoices.
Mr. Davis admitted in May that he prepared false invoices and overbilled the district for a number of maintenance items.
He also submitted false invoices from a printing company, when "he hadn't paid any money; he hadn't ordered any goods.
Jim Devine, 58, was sentenced to 16 months in March for submitting false invoices totalling £8,385.
The executive, Donald Vaillancourt, submitted false invoices over 16 years from fake companies he created, prosecutors said.
Devine is alleged to have claimed £3,240 for cleaning services and £5,505 for stationery using false invoices.
He is also alleged to have used false invoices to claim £1,950 for IT services in 2006.
Outside companies were also said to have filed false invoices to Livent and received payments from the company, the commission said.
Devine is alleged to have claimed £3,240 for cleaning services and £5,505 for stationery using false invoices in 2008 and 2009.
