A laptop used by Poppi Worthington’s father on the night she died contains no evidence of criminal activity, police have said.

Paul Worthington, 50, told police he viewed adult pornography on the computer, which was not seized at the time of Poppi’s death.

The failure to immediately seize the laptop was one of a number of mistakes by Cumbria police in the case. Detectives recovered the computer in July and hoped it may provide vital evidence.

In January a senior coroner concluded on the balance of probabilities that Poppi was sexually assaulted in her father’s bed before her death on 12 December 2012. The coroner found that the 13-month-old suffocated as she slept next to her father in an “unsafe sleeping environment”, and he ruled out penetration as the cause of death.

The finding was the third court judgment against Poppi’s father, who has been investigated several times but has never been charged and maintains his innocence.

Cumbria police said on Friday that although detectives were confident the laptop was being used by Worthington at the time of his daughter’s death, it contained no criminal evidence.

The force said: “The laptop has been subject to meticulous forensic physical and digital examination by accredited forensic examiners in accordance with national best practice. This was subsequently independently assessed by another police force. All examinations resulted in no evidence of criminality being found. The Crown Prosecution Service have been made aware of the results of the laptop examination.”

The conclusion will come as a blow to Poppi’s family, who had hoped the computer could yield a significant breakthrough in the case.Police also lost evidence during their botched investigation.

The CPS said in March that Worthington would not face any legal action and there would be no fourth review of the case without significant new evidence.

Paramedics were called to the Worthington family home in Barrow-in-Furness early in the morning of 12 December 2012. Poppi was taken to Furness general hospital where she was pronounced dead shortly after 7am.

At the latest inquest, in January, Worthington refused to answer 252 questions. His sister said it was on the advice of his lawyers. Poppi’s mother, who cannot be named, believes his silence frustrated the coronial process.

Fiona McGhie, a lawyer at Irwin Mitchell representing Poppi’s mother, said in March: “The past five years have been a complete nightmare for her. Not knowing what happened to Poppi on that day, and knowing that there were evidence-gathering failures by the police in the very early stages of the investigation, has made things even worse.”