HOUSTON — The Justice Department on Tuesday unveiled the first criminal charges in its investigation of the 2010 BP oil spill: two counts of obstruction of justice filed against a former BP engineer accused of destroying records describing the rate at which oil was flowing from the broken well at the bottom of the Gulf of Mexico.

The engineer, Kurt Mix, was involved in efforts to plug the well as well as internal BP efforts to estimate the amount of oil leaking from it in the first months after the spill. Prosecutors allege that Mix deleted two text message strings even after he was told by BP to preserve them.

In one string, Mix allegedly stated that the flow rate on the evening of May 26, 2010, was “over 15,000” barrels per day. At the time, prosecutors note, BP’s public estimate of the rate was 5,000 barrels per day.

The charges show that federal prosecutors are not only interested in the handling of the drilling operation before the April 20, 2010, Deepwater Horizon explosion that killed 11 men, but also in the actions company officials took afterward, as crude gushed from the undersea well for 89 days, wreaking environmental havoc and a public relations catastrophe for the British oil giant.

The charges did not offer much of a hint as to how extensive the criminal reckoning could eventually be.

David Uhlmann, an environmental law professor at the University of Michigan, said Tuesday that obstruction of justice charges are appropriate when there is destruction of evidence during a criminal investigation. But he said he found it “somewhat curious” that “after a two-year criminal investigation the Justice Department chose to lead off with these charges.”

“It leaves unanswered the broader question about whether BP and the other companies involved will be criminally charged for the spill itself, as well as the question of whether any more senior corporate officials will be charged in the case,” he said.

Uhlmann, a former chief of the Justice Department’s environmental crimes section, said that BP’s actions before the spill should be “at the heart of the government’s case.”

Criminal charges in this category could come not only under the Clean Water Act, but the Seaman’s Manslaughter Statute, for the deaths of the 11 workers, and the Migratory Bird Treaty Act, for the death of wildlife, he said.

BP has already reached a proposed settlement with thousands of private plaintiffs for economic damages and medical claims arising from the spill that the company estimates will total $7.8 billion.

Environmental advocates praised the government charges against Mix on Tuesday. They were also quick to point out that the question of how much oil spilled into the gulf is central to the separate civil case the Justice Department has brought against BP.

If that case goes to trial, the total amount of oil spilled – along with the degree to which BP is determined to have acted negligently – will determine the civil penalties the company has to pay under the Clean Water Act.

The government estimates the total spilled and not recovered to be 4.1 million barrels. In the worst case for BP, that would translate into more than $17 billion in fines.

BP has argued that the total is smaller. But David Pettit, a senior attorney with the Natural Resources Defense Council, said any evidence that BP workers misrepresented the flow rate could work against the company as it makes that case.