Hun Manet has hired a law firm to contest a lawsuit that has been brought against him in the US by the family of an opposition activist imprisoned in Cambodia.

According to court documents, Lieutenant General Manet, eldest son of Prime Minister Hun Sen, plans to appear at a hearing in California scheduled for September 1 in a bid to have the case dismissed, and will be represented by John Purcell, of Los Angeles-based law firm Quinn Emanuel Urquhart & Sullivan.

In a complaint lodged April 8 at the US District Court Central District of California, the family of Cambodia National Rescue Party official Meach Sovannara – who is also a US citizen – accused Manet, head of the Defence Ministry’s anti-terrorism unit, of wrongful imprisonment amounting to torture.

The suit, which also names the Cambodian government as a defendant, relates to the opposition member’s imprisonment for “incitement” over a 2014 anti-government protest at Freedom Park in Phnom Penh that turned violent. Sovannara yesterday appealed the verdict.

It alleges Manet’s family connections and leadership role within Cambodia’s security forces make him liable for the emotional and financial damage borne by Sovannara’s family, who live in Long Beach, California.

The city is also where process server Paul Hayes attempted to serve Manet with a summons for the case during a US tour by the scion earlier this year.

The April 9 incident outside La Lune restaurant, which resulted in Hayes’ alleged assault by Manet’s bodyguards as he tried to approach their boss, now forms a core component of arguments by both parties as to what the court should do next.

In a motion of dismissal, Manet’s attorney Purcell argues Hayes failed to properly serve his client, but also further contends the court does not have any other grounds for personal jurisdiction over Manet.

Purcell points to Hayes’s recollection in his affidavit that he was about “5 to 10 feet” from Manet, extending the papers in his left hand and calling “General Manet, General Manet”, when he was grabbed and prevented from delivering the documents to his target.

“Manet was never served (or even informed of the lawsuit) by the process server,” it reads.

In a declaration filed with the court, Manet also claims he was unaware he was being served and had rushed into the bathroom to wash his face after pepper spray was dispersed over the crowd, which included anti-government protesters.

Sovannara’s team, meanwhile, intends to ask the court to assess issues surrounding whether the case can be heard via “jurisdictional discovery” proceedings.

In particular, they suggest Manet, via his bodyguards, “unlawfully acted to interfere” with Hayes’s service through a “violent physical assault on the process server”, and say this requires “further exploration”.

Their motion claims to have video and photographic evidence showing Manet was served by Hayes, whose assault is being investigated by police.

US-based attorney Morton Sklar, who represents Sovannara’s family, said, if granted, the motion would open the Cambodian government to “very probing questions”.

But in a counter-motion, Manet’s lawyer calls the request a “waste of the court’s time”.

“The plaintiffs’ speculation about a scheme to prevent service is ‘little more than a hunch’ and is insufficient reason to put Manet to the cost and inconvenience of answering to the Plaintiff’s fishing expedition.”

Manet could not be reached.