(CNN) -- A sailor found dead earlier this week at California's Camp Pendleton was shot while standing sentry, and a fire was set in an attempt to cover up evidence, the U.S. Navy said.

Seaman August Provost, shown on his MySpace page, was killed while on sentry duty at Camp Pendleton.

The death of Seaman August Provost of Houston, Texas, is being investigated as a homicide, Capt. Matt Brown told reporters on Thursday. A sailor is in custody in the case, Brown said.

Although at least one of Provost's relatives said she believes he was killed because of his sexual orientation and his race, Brown said there was no indication the killing was a hate crime. A U.S. congressman also said on Friday there are indications Provost may have been killed because of his sexual orientation.

Provost was killed while he was standing guard as a sentry for the Assault Craft Unit 5 compound at Camp Pendleton, Brown said. He had begun the shift at 11:30 p.m. Tuesday, and his body was discovered by his replacement around 3:30 a.m. Wednesday.

"Preliminarily, it appears that Seaman Provost suffered gunshot wounds and it appears that someone attempted to destroy evidence by lighting a fire at Seaman Provost's assigned place of duty," Brown said.

Provost's aunt, Rose Roy, of Beaumont, Texas, said by telephone on Friday that her nephew had told her he was being harassed because of his sexual orientation and because he was African-American. She described him as bisexual.

"He mentioned it to me and a couple other family members," she said of the harassment, and said he had first told her about it sometime last year.

"He was frustrated by it," she said. She said she had advised him to speak to someone of higher rank, but said she wasn't sure if he had done so.

"He went to serve and protect, but he didn't get the protection," she said. Brown said Thursday that he had no information on claims of harassment.

Asked whether she believed her nephew was killed because of race and sexual orientation, she said, "In my heart, I do." She added, "it was like an execution-style killing, and nobody does that unless you have that kind of hatred in your heart."

The Navy has one sailor in custody who "has been linked to the commission of this crime through both physical evidence and his own statement," Brown said. Watch Brown talk about the killing as a random act »

He did not identify the sailor, who has not been charged with wrongdoing. It is unclear if the sailor served with Provost in the same unit.

A second sailor whom authorities initially questioned has since been released, Brown said.

He said the Navy has no indication that Provost's death is a hate crime, although he emphasized the investigation is ongoing.

"What I can tell you, unequivocally at this point, based on the preliminary information that we have, is that regardless of the person standing watch in that sentry station, this crime would have most likely been carried out in the same way," he said.

"In other words, another sailor could have been on that post and would have been the victim of this crime."

Rep. Bob Filner, a California Democrat, has called for a full and transparent investigation. Asked Friday if Provost was killed because of his sexual orientation, he said, "There are indications that that's the case. His family says he was harassed."

Filner said he was on Camp Pendleton hours after Provost's body was found, although no one told him of the killing.

"When I was on the base for another event, the commander of the base was sitting next to me and never mentioned a word, which I find very strange," he said.

He said he was asking for the "truth of what happened."

"We're going to ask, if I may coin a phrase, and we hope that they tell," he said.

Roy said her nephew was "a good kid," who didn't have a "bad bone in his body" and had loved the Navy. He joined the service in March 2008, according to Brown.

"He was a people person," Roy said. "If he could give you the shirt off his back, he would."

A funeral has been planned for July 10 in Houston, she said.

"We loved him dearly," she said.

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