The fatal knife attack of an 11-year-old boy while he was playing football with friends has put misinformation in the spotlight in Spain after false claims were spread on social media that the suspect was of North African origin or an unaccompanied minor asylum seeker.

The attack occurred on Sunday morning when the child, called Mateo by his family, was among several children playing soccer at a sports center in the small town of Mocéjon in the center of the country. A man with a hood pulled over his head and wearing a headscarf to hide his face ran onto the field with a sharp object in his hand.

The victim’s family later suggested that the attack was random, saying the man first approached another group of young people in the field who managed to escape. He then captured Mateo, who was with two friends, and reportedly stabbed him more than 10 times before fleeing the scene.

After police combed the area using land and air surveillance in an operation lasting over 30 hours, a 20-year-old man was arrested at his father’s house in Mocéjon in connection with the crime.

In the dozens of hours between the attack and the arrest, posts quickly spread on social media with false claims that the suspect was of North African origin or an unaccompanied minor seeking asylum in Spain, similar to the way the recent killings in the English town of Southport were used to stoke anti-immigration tensions.

Among those speaking out was Alvise Pérez, a 34-year-old far-right agitator from Seville who was recently elected to the European Parliament. Pérez, whose political success was based in part on his tough anti-immigrant stance, drew a link on social media between the murder and the arrival of “50 Africans” at a hotel in the area. Pérez was asked for comment.

As misinformation spread online about the attacker’s identity, the victim’s family pleaded with people to let the police do their job. “This has nothing to do with race or ideology,” Asell Sánchez, a relative who acts as a spokesman for the family, told reporters. “They are talking about migrants who came to the hotel. These are peaceful people who are carrying on with their lives. This has nothing to do with that.”

Instead, he pointed to evidence that suggested the attacker had entered the sports center through a broken back door, suggesting the attack had been carried out by someone who knew the area. Nevertheless, views of misleading posts continued to mount, although police sources made it clear in Spanish media that they had ruled out a jihadist link to the murder.

Sánchez later broke down in tears as he recounted how the misinformation had led to him becoming the target of online attacks. “It was terrible,” he told Cope. “I did it out of love for my family and I’m being criticised on social media for it, they’re attacking me. They’re looking into my past – I don’t have a past, I worked in the media.”

He added: “They take things out of context and tell me I have dirty hands because I have pictures from Africa (on social media). It’s really difficult.”

The hate crimes unit of the Spanish public prosecutor’s office said it was investigating several of the messages circulating that sought to criminalise foreigners and incite “feelings of hatred, hostility and discrimination” towards certain groups.

On Tuesday, a day after Spanish media published images apparently showing the arrest of a young white man in connection with the crime, the Spanish government’s representative in the Castile-La Mancha region stressed how disinformation had exploited people’s emotions in a case that is currently shaking Spain.

Milagros Tolón condemned those who knowingly spread false claims, calling them “hatemongers who took advantage of human suffering, such as the death of an 11-year-old child, to vent all their hatred on social media.”

Speaking to reporters, she described social media as a “dumping ground for filth” because a group of mostly anonymous users try to blame people based on the colour of their skin or religion. Others try to spread untruths just to enrich themselves, she added, without going into further detail.

“Can anything be more cruel and pathetic?” she said. “I urge the hate preachers to be human and act like human beings. Their misinformation causes harm and can provoke anger in innocent people. You cannot exploit one tragedy to create another.”