BERLIN (AP) — Senior politicians in Germany expressed shock over the weekend killing of a young gas station clerk who asked a customer to wear a face mask, and they warned Tuesday against the radicalization of people who oppose the country's pandemic restrictions.

A 49-year-old German man was arrested in the fatal shooting of the clerk Saturday in the western town of Idar-Oberstein. The suspect is being held on suspicion of murder.

Authorities said the man told officers he acted “out of anger” after being refused service for not wearing a mask while trying to buy beer.

“He further stated during interrogation that he rejected the measures against the coronavirus,” the Trier police department said in a statement.

A requirement to wear masks in stores is among the measures in place in Germany to stop the spread of the virus.

According to police, the suspect left the gas station after the dispute but then returned a half-hour later wearing a mask and fatally shot the 20-year-old clerk in the head.

The suspect, a German citizen who wasn't identified by name in line with privacy laws, fled the scene and turned himself in to police on Sunday morning.

The center-left Green party’s candidate to succeed German Chancellor Angela Merkel voiced dismay at the killing. Germany's federal election is scheduled for Sunday.

“I’m shaken by this terrible murder of a young man who merely asked that existing rules be followed,” Annalena Baerbock said in a tweet.

Baerbock also expressed concern about the radicalization of Germany's Querdenken movement, which includes people who oppose masks and vaccines, conspiracy theorists and some far-right extremists.

Authorities didn't immediately say whether the suspect in the gas station killing was associated with the movement, which has come under increasing scrutiny from Germany's security services following a series of large antigovernment protests, some of which turned violent.

Prosecutors told Germany's dpa news agency that the man wasn't previously known to police and that he wasn't legally entitled to possess the firearm found at his house.

Paul Ziemiak, the general secretary of Merkel's center-right Christian Democratic Union party, called the clerk's slaying “incomprehensible.”

“A young man was virtually executed because he pointed out the mask requirement,” Ziemiak said on Twitter. “An inconceivable level of radicalization!”

The head of the domestic intelligence agency in the eastern state of Thuringia, Stephan Kramer, told Germany's RND media group that the killing was “no surprise to me in view of the steady escalation in recent weeks.”

Kramer said his office had warned of the growing potential for violence.

“It's regrettable that someone always has to die before the risk is taken seriously,” he was quoted as saying. "

Facebook last week removed almost 150 accounts and pages linked to the Querdenken movement under a new policy focused on groups that spread misinformation or incite violence but which didn't fit into the platform’s existing categories of bad actors.

Frank Jordans, The Associated Press