A German man has admitted kidnapping and murdering a four-year-old refugee boy, who had also reportedly been sexually abused.

The 32-year-old suspect, who has not been named, confessed to killing another child after being arrested yesterday at his family's home in Brandenburg, near Berlin.

Police had been waiting for him to arrive after his mother turned him in.

A man lights a candle at a memorial site for the killed 4-year-old Bosnian migrant boy Mohamed Januzi at the State Office of Health and Welfare (Lageso) in Berlin, Germany, on 30 October (AP)

A spokesperson for the state prosecutor said his previous victim was a six-year-old boy called Elias, who went missing while playing near his parent’s house in nearby Potsdam in July.

German media reported that Elias’ body had been buried at an allotment, where police are now said to be digging to recover his remains.

A huge investigation had been launched after the boy vanished but CCTV analysis, interviews, public appeals for information and search operations from the air, land and in rivers had not found a trace.

Mohamed disappeared from outside a refugees’ reception centre on 1 October and was seen on CCTV footage leaving with an unidentified man, being led away while holding his hand.

Police are digging in an allotment in Luckenwalde to find the body of the man's previous victim (AFP/Getty Images)

The four-year-old’s decomposing body was found in the boot of the suspect’s car yesterday after the man was reported to police by his mother.

Investigators said that the suspect told them he had killed the boy the day after his abduction but did not elaborate on how he died.

Mohamed was from Bosnia and Herzegovina and had been waiting outside the Lageso reception centre with his mother and siblings as the family waited to be registered, Berlin authorities said.

Refugees settle in Germany Show all 12 1 /12 Refugees settle in Germany Refugees settle in Germany Germany Mohamed Zayat, a refugee from Syria, plays with his daughter Ranim, who is nearly 3, in the one room they and Mohamed's wife Laloosh call home at an asylum-seekers' shelter in Vossberg village on October 9, 2015 in Letschin, Germany. The Zayats arrived approximately two months ago after trekking through Turkey, Greece and the Balkans and are now waiting for local authorities to process their asylum application, after which they will be allowed to live independently and settle elsewhere in Germany. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity 2015 Getty Images Refugees settle in Germany Germany A refugee child Amnat Musayeva points to a star with her photo and name that decorates the door to her classroom as teacher Martina Fischer looks on at the local kindergarten Amnat and her siblings attend on October 9, 2015 in Letschin, Germany. The children live with their family at an asylum-seekers' shelter in nearby Vossberg village and are waiting for local authorities to process their asylum applications. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity Getty Images Refugees settle in Germany Germany Kurdish Syrian asylum-applicant Mohamed Ali Hussein (R), 19, and fellow applicant Autur, from Latvia, load benches onto a truckbed while performing community service, for which they receive a small allowance, in Wilhelmsaue village on October 9, 2015 near Letschin, Germany. Mohamed and Autur live at an asylum-applicants' shelter in nearby Vossberg village. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity Getty Images Refugees settle in Germany Germany Mohamed Ali Hussein ((L), 19, and his cousin Sinjar Hussein, 34, sweep leaves at a cemetery in Gieshof village, for which they receive a small allowance, near Letschin Getty Images Refugees settle in Germany Germany Mohamed Zayat, a refugee from Syria, looks among donated clothing in the basement of the asylum-seekers' shelter that is home to Mohamed, his wife Laloosh and their daughter Ranim as residents' laundry dries behind in Vossberg village on October 9, 2015 in Letschin, Germany. The Zayats arrived approximately two months ago after trekking through Turkey, Greece and the Balkans and are now waiting for local authorities to process their asylum application, after which they will be allowed to live independently and settle elsewhere in Germany Getty Images Refugees settle in Germany Germany Asya Sugaipova (L), Mohza Mukayeva and Khadra Zhukova prepare food in the communal kitchen at the asylum-seekers' shelter that is their home in Vossberg village in Letschin Getty Images Refugees settle in Germany Germany Efrah Abdullahi Ahmed looks down from the communal kitchen window at her daughter Sumaya, 10, who had just returned from school, at the asylum-seekers' shelter that is their home in Vossberg Getty Images Refugees settle in Germany Germany Asylum-applicants, including Syrians Mohamed Ali Hussein (C-R, in black jacket) and Fadi Almasalmeh (C), return from grocery shopping with other refugees to the asylum-applicants' shelter that is their home in Vossberg village in Letschin Getty Images Refugees settle in Germany Germany Mohamed Zayat (2nd from L), a refugee from Syria, smokes a cigarette after shopping for groceries with his daughter Ranim, who is nearly 3, and fellow-Syrian refugees Mohamed Ali Hussein (C) and Fadi Almasalmeh (L) at a local supermarket on October 9, 2015 in Letschin, Germany. All of them live at an asylum-seekers' shelter in nearby Vossberg village and are waiting for local authorities to process their asylum applications, after which they will be allowed to live independently and settle elsewhere in Germany 2015 Getty Images Refugees settle in Germany Germany Kurdish Syrian refugees Leila, 9, carries her sister Avin, 1, in the backyard at the asylum-seekers' shelter that is home to them and their family in Vossberg village in Letschin Getty Images Refugees settle in Germany Germany Somali refugees and husband and wife Said Ahmed Gure (R) and Ayaan Gure pose with their infant son Muzammili, who was born in Germany, in the room they share at an asylum-seekers' shelter in Vossberg village on October 9, 2015 in Letschin, Germany. Approximately 60 asylum-seekers, mostly from Syria, Chechnya and Somalia, live at the Vossberg shelter, which is run by the Arbeiter-Samariter Bund (ASB) charity, and are waiting for authorities to process their application for asylum 2015 Getty Images Refugees settle in Germany Germany German Chancellor Angela Merkel pauses for a selfie with a refugee after she visited the AWO Refugium Askanierring shelter for refugees in Berlin Getty Images

They have not speculated on a motive, but said there is no evidence that the suspect was xenophobic or had links to far-right groups.

Increasing violence is being directed at refugees in Germany, where centres and housing have been daubed with neo-Nazi graffiti and set on fire, while politicians supporting the resettlement of asylum seekers have been attacked.

Aid agencies have long warned of the dangers faced by children among the hundreds of thousands of asylum seekers journeying from the Middle East and Africa to Europe.

“The response to this crisis at the European level is progressing at a painstakingly slow pace,” a spokesperson for Save the Children said, listing dangers including sexual abuse, violence, exploitation and trafficking.