Officers who responded to a call about why an illuminated Christmas tree was still on display found themselves unexpectedly involved in a murder investigation, police said on Monday.

A female passer-by spotted the tree through a house window in the eastern German town of Merseburg. She called officers to register her curiosity about why it hadn't yet been taken down.

Police entered the house to investigate and discovered an elderly woman's body in the cellar.

Arrest made, investigation launched

The woman, believed to be aged 76, appeared to have been the victim of violent crime and had died a considerable time previously.

Read more: Wife confesses to husband's unsolved 2008 murder

Police in the nearby city of Halle, in the state of Saxony-Anhalt, said they had taken the woman's 51-year-old son into custody on suspicion of murder. The arrest was made at the house in question.

"At the moment it remains completely unclear what led to the death of the woman," police spokeswoman Antje Hoppen told the Mitteldeutsche Zeitung newspaper. "Investigations have only just begun."

Prosecutors have applied for the man to be held in custody, with police organizing a forensic examination of the body.

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