The criminal trial of 36-year-old Scott Warren, of Ajo, Arizona, began Wednesday at the US District Courthouse in Tucson

A humanitarian aid volunteer who gave food, water and other supplies to undocumented migrants that crossed the US southern border into Arizona is facing up to 20 years in federal prison.

Scott Warren, 36, of Ajo, Arizona, was arrested by US Border Patrol agents on January 17, 2018, along with two undocumented men: Kristian Perez-Villanueva of El Salvador and Arnaldo Sacaria-Goday of Honduras.

Prosecutors charged Warren with three counts of harboring and conspiring to harbor illegal aliens. His trial began Wednesday at the US District Courthouse in Tucson.

Warren is a volunteer for No More Deaths - an aid group that leaves potentially life-saving supplies for migrants traversing Arizona's desolate Sonoran Desert after they have crossed the US border from Mexico.

Warren (pictured, right) is a volunteer worker with No More Deaths, an Arizona-based humanitarian aid group that leaves supplies for migrants traversing Arizona's desolate Sonoran Desert

Activists insist that they are saving lives by leaving water for migrants crossing the 100,000 square-mile Arizona desert, where temperatures can reach as high as 125 degrees in the daytime during summer months

He's one of at least five No More Deaths volunteers to be prosecuted by federal law enforcement officials since the Trump administration began arresting the southern border humanitarian activists in 2017.

The two migrant men Warren was arrested with showed up at No More Deaths' base of operations in Ajo, known as 'the Barn,' as Warren was arriving back from a grocery store, according to Tuscon.com.

The men said they'd only consumed sports drinks and a burrito during their grueling two-day trek across the desert region. Warren cooked them a meal, gave them clothes and let them reside at the Barn for three days before US Border Patrol agents arrived and arrested all three of them.

No More Deaths has said Warren's arrest was federal authorities' response to the aid group releasing a video showing border patrol agents destroying water jugs that the activists had left for migrants.

Jugs of water for undocumented immigrants sit along migrant trails after being delivered by volunteers for the humanitarian aid group No More Deaths on May 10 near Ajo, Arizona

Scott Warren deliverers food and water along remote desert trails used by migrants

They point out that Warren was arrested mere hours after the video was released.

US Attorney Nathaniel Walters said Warren's case 'is not about humanitarian aid,' but rather about whether or not Warren 'intended to violate the law,' by shielding Perez-Villanueva and Sacaria-Goday from border patrol agents.

'No More Deaths is not on trial. Scott Warren is,' Walters said.

Warren's defense attorney, Gregory Kuykendall, told the court his client is a 'law-abiding, life-giving Good Samaritan,' who 'never gave [the migrant men] anything besides basic human kindness.'

Warren's supporters, including his parents Mark and Pam, hosted a rally outside the courthouse.

Warren's supporters raised signs outside the US District Courthouse in Tucson, Arizona

Scott Warren's parents, Mark and Pam, addressed their son's supporters during a rally

'We were crushed to learn that he was facing serious federal charges that could result in his incarceration for many years,' Mark Warren told the crowd. 'We had always been concerned, worried as parents about his work in a dangerous and tumultuous region. We just never imagined that one of the great dangers he faced was from our own government.'

US Border Patrol agents John Marquez and Brendan Burns told the court they began surveillance of Warren at the Barn for the first time on the day of his arrest.

They said they were looking for two suspected undocumented migrants who had been spotted wandering around a local gas station.

Surveillance video showing Perez-Villanueva and Sacaria-Goday buying sports drinks, food and cigarettes at the gas station and hanging out in a cafeteria area was shown to the court, according to the Tucson Sentinel.

Burns told the jury that while he was surveilling the Barn, he saw Warren pointing out landmarks to the migrant men that would help them avoid Border Patrol checkpoints.

Warren could be sentenced to up to 20 years in prison if convicted of the federal charges against him

Burns said the he and his fellow agent radioed for backup before raiding the facility and arresting the suspects.

Warren's attorney, Kuykendall, seized on the agents' testimony that descriptions of Perez Villanueva and Sacaria-Goday were given to them by other agents who arrested another migrant man a day prior.

'They matched their description? Or they matched the description of two brown people?' the attorney asked.

'In my experience, they were other-than-Mexican... In my mind, these could possibly be them,' Marquez replied.

'You didn't know anything about them other than, they were not Mexican, isn't that true?' Kuykendall responded.

Scott Warren (center) leads a group of student volunteers delivering food and water along remote desert trails used by undocumented immigrants in May

Marquez replied no, according to the Tucson Sentinel.

Warren's trial is scheduled to resume at 2.30pm on Monday.

The bodies of more than 3,000 migrants have been found in the southern Arizona desert since 2001, according to data collected by the Arizona Open GIS Initiative.

Temperatures in the 100,000 square-mile region can reach as high as 125 degrees in the daytime during summer months.

There were 127 migrants found dead in the desert in 2018. Migrant deaths in the region have skyrocketed since 2000 when the remains of just one border crosser were recovered, according to the Arizona Republic.

Most who are found are never identified so they can be returned to their families.

'People are dying right on the edge of our town. That's what drives me to act,' Warren' told the New York Times during a recent interview.

'The government is responsible for the crisis of death and disappearance... If you stop people from putting water in the desert, that's going to make the desert even more deadly.'