"I’m so worried he kills himself and others in the quest to boost his ego," David Lochridge said of the company's CEO in the note.
The recovered debris and evidence from the submersible will be sent for further testing and analysis.
The agency has convened a Marine Board of Investigation, its highest-level probe.
Christine Dawood was on board the host ship when the submersible carrying Suleman and Shahzada Dawood to the Titanic lost communications.
Jay Bloom said he turned down repeat invites to participate in Sunday's dive with his son, who expressed concerns about the vessel's safety.
Ex-US president referenced the Greek boat tragedy which saw hundreds of refugees die last week.
The announcement follows the search team finding debris near the Titanic wreckage that appeared to be from the Titan vessel.
One of the biggest games of this generation just got bigger.
The craft has made its last close flyby of Saturn's moon.