The family of a 12-year-old child killed in a suspected hit and run outside a school have paid tribute to their “kind, helpful and lovely boy”.

He was formally identified on Tuesday as Harley Watson, a pupil at Debden Park high school, moments after Essex police revealed it had referred itself to the Independent Office for Police Conduct (IOPC) over previous contact between its officers and an arrested suspect in the case.

“We are so devastated by what has happened,” Harley’s family said on Tuesday evening. “Harley was a good, kind, helpful and lovely boy. We would like to thank everyone for their kind wishes and concern. However as a family we would like people to respect our privacy and allow us to grieve in peace.”

Earlier, it emerged that detectives were looking into suggestions the suspect may have tried to carry out a similar attack at another school moments earlier.

Officers confirmed they had received reports of a car mounting the pavement outside Roding Valley high school in Loughton about 10 minutes before Harley was killed on Monday. They said the first incident was reported to officers “after it became widely known we were dealing with a serious collision” outside Debden Park high school.

“Our investigations have led us to establish that there may be connections between that incident and the one which has led us to establish a murder investigation,” Essex police said.

Four other teenagers and a woman in her 20s received non-life-threatening injuries in the second incident.

Tributes were left at the scene on Tuesday, with dozens of bouquets and handwritten cards addressed to Harley, the “funniest” boy, adorning the school wall. “Forever in our heart. Fly high,” read one. “You will be missed, it won’t be the same without you,” another said.

Eli Claarson, 12, and his mother, Simone, came to lay flowers and pay their respects. “I went to primary school with Harley,” Eli said. “We haven’t seen each other since year 6 but we still chatted online. It’s so sad to know he’s gone. He was so caring and would never have done anything to anyone.” Simone added: “As a parent, it really makes me concerned about the kids. I worry for them getting home after school.”

Christian Cavanagh, the executive headteacher of Debden Park high, said Watson “had made his mark on the school” and was “liked and loved by staff and students”.

Sandra Lyfield, 68, who lives close to the school, said: “It’s shocking when something like that happens around here. Even if you don’t know the people, it’s just horrible. It chokes you up. I walk my dog down there, and today it’s so sombre, with people crying.”

James English, a 34-year-old resident said: “Everyone’s just really sad. The kids normally play and ride their bikes down here, doing wheelies on the street. Now everyone’s just really sad.” Another resident, who did not wish to give her name, added: “It could be anybody’s child, it’s just horrific.”

Many people wept as they arrived to lay tributes at the school throughout the morning. There was an extensive cordon in place at the scene of the crash, with much of the road closed to the public and a heavy police presence nearby.

The school remained open, and was offering counselling to those affected by the event, while police photographers and investigation teams worked to gather evidence on the street.

A 51-year-old man has been arrested on suspicion of murder, six offences of attempted murder and one offence of causing death by dangerous driving. He was also arrested on suspicion of six offences of causing serious injury by driving, failing to stop at the scene of a collision and of driving without insurance, police said.

Officers said the suspect was found in a vehicle in the car park of a pub about three miles from the scene of the murder at 11pm on Monday. “We have recovered a car and we do have a scene on there currently as part of our ongoing investigations. I am keen to establish the journey the car took from [the school] to the car park of the Merry Fiddler pub,” said the senior investigating officer, DCI Rob Kirby.

Confirming its voluntary self-referral to the IOPC on Tuesday evening, Essex police said it had become “aware of speculation around specific elements of contact between the force and the suspect” but declined to confirm any further details.