Instagram sensation Dan Bilzerian received some bad news when he returned to his West Hollywood mansion after a September break-in — several of his guns were gone.

But it wasn’t burglars who had taken the firearms, it was the Los Angeles Police Department.

For two months after the break-in, Mr. Bilzerian, a professional poker player and gun rights champion, says police inexplicably continued to keep the nine firearms under lock and key without a warrant. When the eight pistols and one rifle were returned to their owner about a week ago, all the ammunition for the firearms was missing, raising questions about the LAPD’s protocol for seizing firearms.

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“All of my ammunition and the magazines were gone. And they couldn’t explain what happened to the magazines, but that ammo couldn’t be released with a firearm and that I’d have to schedule a separate three-hour visit for the ammo,” Mr. Bilzerian told The Washington Times. “If they are gonna take the guns and make me wait for three hours at the police station, they should at the very least return what came with them.”

The break-in occurred in the early morning hours of Sept. 5, a weekend when Mr. Bilzerian was out of town, according to the police report.

The perpetrators disabled security cameras outside the home before breaking a glass window to gain entry. Once inside, the intruders attempted to break into a closet where Mr. Bilzerian kept a collection of firearms, but the steel-reinforced room withstood their attempts.

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Meanwhile an alarm for a security system to the house was triggered, summoning police. The burglars escaped before police arrived, but once on scene, the officers turned their attention to the firearms they believed were in the home.

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It’s unclear exactly why police forced their way inside the closet where the guns were stored. Officers asked Mr. Bilzerian’s assistant and security guard for permission to break into the room but the aides declined, but the officers accessed it anyway, Mr. Bilzerian said.

“They broke into our closet and took them after we were burglarized,” said Mr. Bilzerian’s assistant Jeremy Guymon. “It’s not like we were doing anything wrong.”

The responding officers confiscated nine firearms supposedly under the premise that they wanted to secure the home in case the burglars attempted a second break-in, Mr. Bilzerian said. But strangely, the officers left behind an arsenal of shotguns and a high-powered semiautomatic carbine rifle like the ones used by special operations troops.

“The officers told my assistant that they took the handguns because they didn’t want the suspects to come back and get them on a second break-in even though they were unsuccessful at opening the steel reinforced door the first time,” Mr. Bilzerian said. “Essentially they were ‘trying to protect my property and people’s safety.’ This is hard to grasp, when they left my $21,000 FN SCAR17 with thermal optic and shotguns unsecured in that same room.”

After two months shuffling between prosecutors’ and police offices to retrieve the firearms, Mr. Guymon said it seems unlikely at this point that Mr. Bilzerian will get his ammunition back.

Los Angeles police spokeswoman Officer Norma Eisenman said Wednesday the department was unable to immediately comment on the allegations made by Mr. Bilzerian or the LAPD’s protocol for securing stored guns at the scene of a break-in.

Attorney Joseph A. Silvoso III, a California gun law expert at the law firm Michel & Associates, said he has seen numerous incidents in which police responding to a crime scene confiscate guns without a warrant, either talking victims into permitting the seizure or declaring it was necessary for public welfare or personal safety.

“I can speak to California and there is a mindset, either it is cultural or politically pushed by the leadership, where we are seeing law enforcement responding to a scene where a crime has been committed, then asking for the location of any weapons and the ability to seize the firearms comes up,” he said.

Mr. Silvoso said after the guns are taken by police, it is a cumbersome paperwork process in California for the legal owners to get them back. And Mr. Bilzerian’s experience of not getting his ammunition returned is not uncommon, he added.

“We’ve unfortunately seen law enforcement from different agencies from time to time do that,” he said. “They just say ‘it’s just not safe to hand you back the guns and the ammuniton together’ or drum up some other reason not to return the ammunition or magazines.”

The LAPD’s seizure and handling of firearms from gun owners has raised legal concerns in the past. This year, at least two people have sued the department over its failure to return firearms that were taken from gun owners.

In July, Wayne William Wright filed a $4.8 million lawsuit against the LAPD following nearly 10 years of legal battles over the department’s seizure of more than 400 of the gun collector’s firearms. The guns were taken after police orchestrated a sting operation in 2004 during which Mr. Wright sold a gun illegally to an undercover agent, according to court records filed in the case.

Mr. Wright pleaded guilty to a misdemeanor charge and later sought to retrieve his firearms. The department did return 26 of the seized guns, but claimed that Mr. Wright could not prove he was the rightful owner of the other firearms and refused to return them, according to court documents. In 2013, the department destroyed the firearms despite Mr. Wright’s attempts to reclaim them.

Another man sued the LAPD over a similar issue in April after the department destroyed 11 guns worth an estimated $75,000 after they were seized from his home after a shooting at the residence.

The LAPD took the firearms belonging to Alan Minato, owner of a Los Angeles strip club, in 2010 after a child accidentally shot a sibling at Mr. Minato’s home, the San Gabriel Valley Tribune reported.

Mr. Minato was not charged with any crime related to the shooting and tried to collect the confiscated firearms several times but was told that he would be notified when the guns were available. When he tried to collect the firearms again in 2013, Mr. Minato was told that the guns had been destroyed, the Tribune reported.

Mr. Bilzerian, who has advocated for Second Amendment rights including in a column in The Washington Times, said his experience with the LAPD has only furthered his dislike of the “aggressive and unconstitutional anti-gun stance California has taken with its law-abiding citizens.”