The suspect in the Nottingham triple knife killings is a former student at the University of Nottingham named Valdo Amissão Mendes Calocane, the Guardian understands.

Multiple sources said Calocane was born in Guinea-Bissau and settled in Nottingham as a child.

He is being held in connection with a 90-minute rampage on Tuesday that started before dawn with two 19-year-old students from the university, Grace O’Malley-Kumar and Barnaby Webber, being stabbed in the street. The attacks continued with the stabbing of 65-year-old Ian Coates, whose van was stolen and driven into pedestrians.

The university said it was devastated by the news that the 31-year-old suspect was a former student. Police said they did not believe the link was connected to the attacks or explained the motive behind them.

Calocane remains in custody and on Wednesday magistrates granted detectives an extension to hold him until Friday.

Counter-terrorism officers are part of the investigation and electronic devices linked to the suspect – including a phone he was carrying when arrested – are being searched. Nothing yet points to an indication of an ideological motive.

He is understood to have a history of mental health issues and was previously known to police. Sources say he came to the UK legally and from no older than seven he settled in Nottingham, where he was educated.

The university said: “We are devastated that the suspect is a former University of Nottingham student. The police have confirmed that this is not believed to be connected with the attack. Our focus remains on supporting the family and friends of Barney and Grace and our wider community. We will continue to support the police in any way we can.”

The home secretary, Suella Braverman, visited the city on Thursday to lay a floral wreath outside Nottingham Council House before an evening vigil.

A handwritten note attached to the flowers read: “In memory of those who lost their lives, those who were injured and everyone who loves them. We are with you and with all the people of Nottingham.”

Nottinghamshire police said that after stabbing Coates, the attacker twice drove into pedestrians.

“He attempted to run over a man in the Milton Street area, who remains in a serious condition in hospital. He then tried to run over two other pedestrians in the Sherwood Street area who are believed to have suffered minor injuries,” police said.

The force said because its officers were behind the van when this happened, it had referred this incident to the Independent Office for Police Conduct, the police watchdog.

An IOPC spokesperson said: “We received a referral from Nottinghamshire police on Wednesday informing us that a marked police car had been following behind the suspect’s van for a short distance at the time it collided with two pedestrians in the area of Sherwood Street in the city centre on Tuesday morning. We are assessing the referral to decide what further action may be required of the IOPC.”

Calocane was arrested after the van stopped, and officers used a stun gun as they took him into custody.