The missing heart of a dead Marine from Chester County is at the center of an international mystery that threatens to entangle two governments in a Philadelphia court battle.

On Monday, the family of Sgt. Brian LaLoup, a 21-year-old embassy security officer who killed himself last year while stationed in Athens, Greece, accused officials there of removing his heart during an illegal autopsy. Later, they said, Greek officials tried to pass off another heart as their son's.

And while U.S. military officials knew LaLoup's remains were incomplete, they let his body be buried anyway and lied to his parents about it, a lawyer for his family contends.

"At almost every point along the way, there are serious questions about how this was handled," lawyer Aaron Freiwald said.

Last week, the parents, of Coatesville, sued the Defense Department and the Navy in federal court here, alleging negligence and mistreatment of their son's remains. They said in an interview Monday that they were still weighing their legal options against government entities in Greece.

"The ideal outcome for us would be to know the truth for Brian," his mother, Beverly, said through tears. "To say it's been a rough time is an understatement."

Christos Failadis, a spokesman at the Greek Embassy in Washington, expressed sympathy for the family but maintained that the matter was resolved. "This was a very sad event for a young soldier," he said. "But our ambassador has been in touch with his mother some time ago; we thought that it was over."

Representatives for the Defense and State Departments did not return calls seeking comment.

In four years as a Marine, LaLoup served at the U.S. Embassy in South Africa, guarding dignitaries such as Michelle Obama, and was assigned to Athens three months before his death.

On Aug. 12, 2012, after a night of drinking, he shot himself in the head with a service weapon procured from an unlocked storage room in the embassy compound. Earlier that night, he had told other officers of suicidal thoughts and was overheard saying, "I don't have anyone who loves me," the suit alleges.

The events that followed that night were baffling, the LaLoups' lawyer said.

A Greek government-run hospital in Athens performed an autopsy. Only after LaLoup's body reached the U.S. military mortuary in Dover, Del., and a second autopsy was done did American officials notice the heart's absence, Freiwald said.

"Instead of being honest and up front with the family and taking the appropriate action to have the heart returned, [the U.S. military] decided to lie and conceal this fact," the family's suit says.

The Navy initially told the LaLoups that parts of their son's scalp were missing. Only when Beverly LaLoup inquired what would happen if they were later recovered did an official "accidentally" let slip that the scalp was intact but the heart was missing, she said.

By then, she had already buried her son.

"I asked him why we were told it was parts of his scalp," Beverly LaLoup said. "His reply was that they were not going to tell us because that is not something you tell a grieving mother."

The suit seeks more than $225,000 in damages. More than money, the LaLoups hope a federal judge can find answers.

What happened to their son's heart is only one of their questions. Among the others: Why was he encouraged to keep drinking the night of his death, despite talk of suicide? How was a weapons room left unlocked? And why was his body left in Greek custody when Marine and diplomatic protocol called for it to be returned to U.S. soil before any autopsy?

At one point, Greek officials claimed to have found his heart - and sent it to the United States. But testing revealed that the heart did not match LaLoup's DNA, the suit says.

So whose heart was it?

Failadis, the Greek embassy spokesman, said Monday he did not know the answer.