Swedish police have arrested one more person for suspected involvement in the April 7 attack in Stockholm.

According to the Stockholm District Court on Monday, the person is suspected of terror crime, but police won't share any more details about the investigation.

The Swedish Police and the Swedish Security Service working together arrested the person on Sunday evening, according to a statement issued by the police.

"I can confirm that one person was arrested in connection with this investigation," Simon Bynert, a spokesperson for the Swedish Security Service said.

Defence attorney Karl Harling was appointed to represent the suspect, Swedish public broadcaster SVT reported.

Citing secrecy rules regarding the preliminary investigation, police would not say in which way the person is suspected of being involved in the truck attack that killed four people and injured many more.

Prosecutor Hans Ihrman has until Wednesday at noon to request that the suspect continue to be held in remand, SVT reported, citing Swedish news agency TT.

This was the third arrest made in conjunction with the attack. In addition to Rakhmat Akilov who is suspected of driving the truck, another man was held early on in the investigation. The prosecutor lifted the remand but because the man had already received deportation orders, he was moved to a detention center.

Of the 15 people who were injured in the attack, one person is still being treated in the hospital.

A few hours after the attack on April 7, Rakhmat Akilov, a citizen of Uzbekistan, was arrested in Marsta, a suburb north of Stockholm. During interrogations, he admitted to driving the truck down one of Stockholm's busiest pedestrian streets with the intention of killing innocent people.