A former BP engineer charged with deleting text messages about the company's response to the 2010 oil spill in the Gulf of Mexico faces new allegations that he also deleted voicemails from his phone.

A superseding indictment handed up Wednesday by a federal grand jury in New Orleans accuses Kurt Mix of deleting about 40 voicemails from a supervisor and roughly 15 voicemails from a BP contractor.

Mix, of Katy, Texas, pleaded not guilty in May to two counts of obstruction of justice after he was charged with deliberately deleting more than 200 text messages to and from the supervisor and more than 100 to and from the contractor.

Prosecutors claim he deleted the messages to prevent them from being used in a grand jury's probe of the spill.