RALEIGH, N.C. — Relatives of the three Muslim college students killed in North Carolina are pressing for hate crime charges against the alleged shooter, but legal experts say such cases are relatively rare and can be difficult to prove.

Police in Chapel Hill say they have yet to uncover any evidence that Craig Stephen Hicks acted out of religious animus, though they are investigating the possibility. As a potential motive, they cited a longtime dispute over parking spaces at the condo community where Hicks and the victims lived.

Hicks, 46, is charged with three counts of first-degree murder in the deaths of Deah Shaddy Barakat, 23; his wife, Yusor Mohammad Abu-Salha, 21; and her sister, Razan Mohammad Abu-Salha, 19.

The FBI is now conducting a “parallel preliminary inquiry” to determine whether any federal laws, including hate crime laws, were violated in the case.

Search warrants filed in court Friday showed Hicks listed a dozen firearms taken from his condo unit. The warrants list four handguns recovered from the home where he lived with his wife, in addition to a pistol the suspect had with him when he turned himself in after the shootings. Warrants also listed two shotguns and six rifles, including a military-style AR-15 carbine, and a large cache of ammunition.