German prosecutors are investigating whether the prime suspect in the disappearance of Madeleine McCann was involved in a similar case of a five-year-old girl who went missing in Germany in 2015. Reports on Friday night also said authorities were looking into connections with the disappearance of a six-year-old German boy in Portugal in 1996. The developments came as police reports showed that the suspect, a 43-year-old German rapist and child sex offender identified by Portuguese sources on Thursday as Christian Brückner, allegedly fantasised about abducting and sexually abusing minors in a 2013 online chat. Circumstantial evidence has convinced detectives that Brückner is the strongest suspect yet since the British girl Madeleine disappeared in 2007, aged three. Police in Germany, the UK and Portugal made a major appeal for evidence on Wednesday. Brückner, who is in prison in the northern German city of Kiel serving an unrelated sentence for drug trafficking, is said to have told an acquaintance during a Skype chat in September 2013 that he wanted to “catch something small and use it for days”, according to a report by Der Spiegel. The news magazine also reported that when the acquaintance replied that that would be a dangerous undertaking, Brückner appeared to suggest he had prior experience in this regard: “Oh well, if the evidence is destroyed afterwards.” According to Der Spiegel, police in the eastern town of Stendal, in Saxony-Anhalt, found records of the chat on a computer they confiscated in early 2016 from a property owned by Brückner. The dilapidated former box-making factory was searched as part of an arrest warrant in connection with the 2015 disappearance of a five-year-old girl called Inga Gehricke, who went missing from a family outing to a care home in the same region. According to Der Spiegel, investigators also found child sexual abuse images and girl’s clothing inside a trailer on the property, even though Brückner did not have family of his own. It appears he was not investigated further at the time. The lawyer for Inga’s mother has appealed for police to reopen their investigation into her disappearance. “The file was closed only four weeks after the work began,” Petra Küllmei told the local newspaper Volksstimme. “I consider that lacking in ambition.” A spokesperson for the state prosecutor in Stendal told the Guardian on Friday a preliminary investigation had been opened into whether there was a link between the disappearances of Madeleine and Inga. Inga Gehricke’s case has often been compared to Madeleine’s, given that no trace has been found of either girl and no charges have been brought. In German media, Inga has sometimes been referred to as “the German Maddie”. The blond-haired girl went missing from a stretch of woodland near a church-run assisted-living facility for people with mental health or alcohol problems near Stendal between 6.30pm and 6.45pm on 2 May 2015. Initially, police assumed that Inga had got lost in the forest while trying to gather wood for a barbecue planned for that evening. A reward of €25,000 was offered for any vital clues for the child’s whereabouts. According to Küllmei, on 1 May Brückner was involved in a minor traffic accident at a car park on the A2 motorway, about 100 kilometres from the spot where Inga went missing the next day. German news websites have also reported that authorities are now examining connections to the disappearance of Rene Hasee. According to reports the then six-year-old boy, from Elsdorf, Germany, went missing from a beach in 1996 while on holiday with his family in the Portuguese Algarve. Brückner has been described as a drifter with a dandy-esque manner and a string of past convictions, including for sexual offences and child abuse. In 1994, when he was a teenager, Brückner was convicted of sexual abuse of a child, attempted sexual abuse of a child, and carrying out sexual acts in front of a child. He fled to Portugal with a girlfriend the following year and lived in Praia da Luz. Brückner has been convicted of crimes including theft and drug-dealing, and was allegedly known to have made break-ins at hotels and holiday homes in the Algarve. According to court documents seen by the Guardian, Brückner was convicted in Germany last year of the rape of a 72-year-old American woman in Praia da Luz in 2005, two years before Madeleine disappeared from a hotel in the same area where she was staying with her family. His conviction is under review after defence lawyers argued he had been extradited – this time from Italy, to where he had travelled – on another charge and therefore, under the rules of the European court of justice, cannot be tried for a different crime. In Portugal, Gonçalo Amaral, the detective who led the initial investigation into Madeleine’s disappearance, said last year that a “German paedophile who is in prison right now” was “probably going to be the scapegoat” in the case. Amaral, who was removed from the case in October 2007 after criticising British police involvement and whose book about it sparked a bitter legal battle with the McCanns, told Australia’s Nine Network last April the convicted sex offender was now serving time in Germany but had been investigated and cleared by Portuguese police. “He was investigated at the time and … they discarded him,” he said. “The trailer that he lived in was taken to Germany for testing, but nothing was found there.” While German authorities said on Thursday they believed Madeleine was dead, British police believe there is no direct evidence of this and continue to treat the case as a missing person investigation.