Three people remain in hospital after a rollercoaster derailed at the Gröna Lund theme park on Sunday, killing one woman and injuring nine, regional healthcare services told Swedish news agency TT on Tuesday.

Three children who were injured in the accident have all been able to leave hospital.

The Swedish Accident Investigation Authority (SHK), which is scouring the site for clues, said it had discovered an “anomaly”. Its director-general John Ahlberk told public broadcaster SVT late on Monday that two of the derailed train car’s set of wheels had for yet unknown reasons come loose.

“We went on a platform to be able to see the railway from above. We could follow the train car’s journey and believe to have found the first spot where we’ve been able to see an anomaly,” he said.

“That will be interesting for us to investigate,” he added.

SHK’s investigation could take up to a year.

There is also a separate probe being carried out by a prosecutor at Sweden’s unit for work environment cases, who is investigating whether any criminal charges should be brought against the park.

The specific offences being investigated are labelled as causing the death of another person by negligence, causing bodily harm to another person, or causing danger to another person.

Gröna Lund is also carrying out its own investigation into what happened when its Jetline ride partially derailed at around 11.30am on Sunday. In total, 14 people were on the affected train car, which took some people with it as it fell and was left hanging at a height of around six to eight metres.

The Jetline attraction was originally installed in 1988 and fully renovated in 2000. It, along with all other attractions at Swedish theme parks, must be inspected on a yearly basis. In addition to this, Gröna Lund said it carries out further regular inspections, including every day before the park opens.

It passed the most recent yearly inspection without any comments. But according to the Aftonbladet tabloid, a number of passengers had raised safety concerns after travelling on the rollercoaster in recent weeks.

Gröna Lund will remain closed for “at least a week, in order to be there for friends and family members of those affected and for our employees”, according to a statement on its website.

All those who were at the park on Sunday, as well as those who had booked tickets for the coming week, will have their tickets automatically refunded.

The park has also set up a crisis helpline to support those affected by the accident or those with specific questions about what happened. The number is 010-708 9890, and the line will be open from 9am-4pm all of this week.

Gröna Lund refers those with questions concerning refunds, tickets or similar to its customer service department: 010-708 7000, and adds that it will update social media and its homepage with more information.

A number of rides at other parks in Sweden which are made by the same manufacturer as the Jetline ride were closed on Monday, such as the Godiståget at Kolmården Zoo near Norrköping and the Draken ride at Furuviksparken near Gävle.

The Lisebergbanan ride, also by the same manufacturer, would remain open, Liseberg amusement park in Gothenburg told SVT on Sunday.