A former United States Marine reservist and seven others were sentenced to decades in prison over a shooting last year that wounded a police officer during a demonstration at a Texas immigration detention centre.

On Tuesday, Benjamin Song, the Marine reservist, was sentenced to 100 years in prison, the maximum punishment, for opening fire during a July 4 demonstration outside the Prairieland Detention Center near Dallas.

Seven other defendants received prison terms ranging from 30 to 70 years.

Prosecutors called the crime an act of “terrorism” and said the eight were linked to the leftist activist group antifa, a loosely knit anti-fascist movement that President Donald Trump designated a “domestic terrorist organisation”.

The defence, meanwhile, denied any antifa ties. Family members expressed shock and anger over the stiff sentences.

“I am livid,” said Lydia Koza, whose wife, Autumn Hill, was sentenced to 50 years in prison. “The government wants to take her entire life away because she attended a protest. Nobody died.”

US District Judge Reed O’Connor, one of two judges overseeing the proceedings, said what happened was not a protest but “an assault on democracy”. All but one of the eight defendants sentenced on Tuesday were convicted on terrorism charges.

“The need to deter this type of conduct is high,” O’Connor said.

The case drew attention beyond Texas, as critics warned it could have a wide-reaching impact on protests and free-speech rights under the First Amendment of the US Constitution.

The Justice Department called it the first sentencing of “defendants affiliated with” antifa after Trump signed an executive order designating it as a “terrorist” organisation on September 22.

Prosecutors link protesters to antifa

Trump issued the order even though there is no domestic equivalent to the State Department’s list of “foreign terror organisations”.

Antifa is not a single organisation, but rather an umbrella term for far-left, activist groups that confront or resist neo-Nazis and white supremacists at demonstrations.

“The sentences handed down today make clear that antifa terrorists who attack law enforcement and federal facilities will face swift and uncompromising justice,” Acting Attorney General Todd Blanche said in a statement.

Prosecutors told jurors during the trial that the group’s actions – including bringing firearms, first aid kits and wearing body armour – were signals of nefarious intent.

According to the Justice Department, Song had yelled, “Get to the rifles”, and opened fire, striking a police officer who had just pulled up to the centre.

Lawyers for the defendants have said there was no planned ambush and that protesters who brought firearms only did so for their own protection.

They also argued that the gathering was planned as a late-night demonstration with fireworks to show support for immigrants being held at Prairieland before gunshots broke out.

Some defendants say they weren’t part of the planning

Phillip Hayes, Song’s lawyer, rejected characterisations that the protesters were “extremists” and said his client will appeal the 100-year sentence.

“This is a bunch of kids and young adults who really have a really big heart and really wanted their voice to be heard,” Hayes said. “It was never intended that anybody get hurt. It was never intended that any shots would be fired.”

Prosecutor Frank Gatto urged the judge to impose stiff penalties.

“People with that kind of extremist beliefs need extra time in prison,” Gatto said. “They believe violence is justified.”

Defendants and their family members pleaded for leniency.

Autumn Hill said the gathering “seemed more like a party to me than anything else” and that she and others who participated “didn’t expect or want any violence or destruction of property to occur”.

Hill’s lawyer, Cody Cofer, told the judge there was no evidence she had a gun, nor that she believed in violence to achieve change. He said that after fireworks were set off, she was so conscientious that she made sure to pick up the rubbish left behind before leaving.

Chris Tolbert, defendant Savanna Batten’s lawyer, has said that his client did not bring a firearm, spray-paint or fireworks to the centre, nor did she participate in the planning of the demonstration.

Hill and Batten both received 50-year sentences.

Another protester, Daniel Sanchez Estrada, was not at Prairieland on the night of the shooting or involved in the planning, his lawyer, Christopher Weinbel, said

Sanchez Estrada, who is married to another of the defendants, was convicted only on charges of concealing documents.

Weinbel said his client just moved a box of his own belongings of artwork, poetry, journals and zines after the shooting. Nothing in the box was illegal, Weinbel said.

Sanchez Estrada was sentenced to 30 years in prison.

Other defendants previously pleaded guilty to providing material support to “terrorists” rather than take their case to trial.

Last week, federal prosecutors charged 15 people with impeding the Trump administration’s immigration crackdown in Minnesota.

They claimed the demonstrators were members of antifa, who conspired against the federal government to block arrests and deportations by setting up blockades around government buildings and throwing chunks of ice at federal vehicles, among other actions.