Muslims in New Mexico on Wednesday said they felt shock and shame at the arrest of an immigrant from Afghanistan in connection with the murders of four Muslim men.
Police on Tuesday said they detained Muhammad Syed, 51.
A motive for the killings remains unclear, but police said he might have acted on personal grudges, possibly with sectarian overtones.
Mr Syed denied being involved with any of the four killings when questioned by police, The New York Times reported.
"We're in complete total disbelief. Speechless," said Mula Akbar, an Afghan-American businessman who claimed he helped Mr Syed to settle in the city.
"You know, kind of embarrassed to say he was one of our own."
Mr Syed, a Sunni Muslim, prayed together at Albuquerque's Islamic Centre of New Mexico mosque with most of the victims, three of whom were Shiite.
All four were of Afghan or Pakistani descent. One was killed in November, the other three in the past two weeks.
Mr Syed, who made his first appearance in court on Wednesday, was formally charged with killing Aftab Hussein, 41, on July 26 and Muhammed Afzaal Hussain, 27, on August 1.
Police said on Tuesday that they were working with prosecutors on potential charges for the murders of Naeem Hussain, 25, a lorry driver killed on Friday, and Mohammad Ahmadi, 62, shot dead on November 7, 2021, outside the grocery shop he ran with his brother in south-east Albuquerque.
It was not immediately clear if Mr Syed had a lawyer. Local TV station KRQE News 13 quoted his family as saying they believed he was innocent.
Palestinian-American Samia Assed said the Muslim community of about 4,000 in the city of more than 500,000 people had work to do to prevent the violence they left behind in countries such as Afghanistan and Pakistan.
"This took me back to 9/11 when I just wanted to hide under a rock," said Ms Assed, a human rights activist, after she hosted an interfaith memorial at the Islamic Centre of New Mexico, Albuquerque's oldest and largest mosque.
"For this to happen it's like setting us back 100 years."
The mosque's congregation is mainly Sunnis from more than 30 countries and they say they have never before experienced violence of this kind.
Police on Tuesday declined to comment on rumours saying Mr Syed was angry that one of his daughters had eloped with a Shiite man.
Mr Syed is also a lorry driver, has six children, is from Pashtun ethnicity and arrived in the US as a refugee about six years ago from Afghanistan's southern Kandahar province, Mr Akbar said.
Mr Akbar is a former US diplomat who worked on Afghan issues and helped to found the Afghan Society of New Mexico.
Mr Syed developed a record of criminal misdemeanours over the past three or four years, including a case of domestic violence, police said.
Video from February 2020 showed him slashing the tyres of a vehicle believed to be owned by the family of the first known victim, Ahmadi, according to the mosque's president, lawyer Ahmad Assed.
"We're in a surreal time trying to make sense of these senseless killings we've suffered," Mr Assed said.
